WORKS  OF  PROF.  A.  F.  HOLLEMAN, 

Professor  Ordinarius  in  the  University  of 
Amsterdam,  Netherlands, 

PUBLISHED    BY 

JOHN  WILEY  &  SONS,  INC. 

A  Text -book  of  Inorganic  Chemistry.  " 

Issued  in  English  in  co-operation  with  HERMON 
CHARLES  COOPER.  Fourth  English  edition,  com- 
pletely revised.  8vo,  viii  + 505  pp.,  79  figures.  Cloth, 
$2.50. 

A  Text-book  of  Organic  Chemistry. 

Edited  by  A.  JAMIESON  WALKER,  Ph.D.  (Heidel- 
berg) B.A.,  Head  of  the  Department  of  Chemistry, 
Technical  College,  Derby,  England,  assisted  by 
OWEN  E.  MOTT,  Ph.D.  (Heidelberg),  with  the  co- 
opera^ion  of  the  author.  Fourth  English  Edition, 
partly  rewritten.  8vo,  xviii-f-619  pp.  82  figures. 
Cloth,  $2.50. 

A  companion  volume  to  the  preceding,  and  forming 
with  it  a  comprehensive  treatise  on  pure  Chemistry. 

A  Laboratory  Manual  of  Organic  Chemistry  for  Be- 
ginners. 

An  Appendix  to  the  author's  Text-book  of  Organic 
Chemistr  .  Edited  by  A.  JAMIESON  WALKER,  Ph.D. 
(Heidelberg),  B.A.,  Head  of  the  Department  of 
Chemistry,  Technical  College,  Derby,  England. 
With  the  co-operation  of  the  author.  Second  English 
Edition,  partly  rewritten.  12mo,  xvii+82  pp. 
Cloth,  $1.00  net. 


A  TEXT-BOOK: 


OF 


ORGANIC     CHEMISTRY. 


BY 

A.  F.  HOLLEMAN,  Ph.D.,  F.R.A.Amst, 

Professor  Ordinqrius  in  the  University  of  Amsterdam. 


EDITED     BY 

A.  JAMIESON  WALKER,  Ph.D.   (Heidelberg),  B.A? 

Read  of  the  Department  of  Chemistry,  Technical  College,  Derby,  England. 

ASSISTED   BY 

OWEN  E.  MOTT,  Ph.D.  (Heidelberg).1 


WITH  THE   CO-OPERATION   OF   THE   AUTHOR. 


FOURTH  ENGLISH  EDITION,  PARTLY  REWRITTEN. 

TOTAL    ISSUE,   THIRTEEN   THOUSAND. 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:   CHAPMAN   &  HALL,   LIMITED 

1914 


Copyright,  1903,  1907,  1910,  1913, 

BY 
A.  JAMIESON  WALKER. 

(Entered  at  Stationers'  Hall.) 


CHRONOLOGICAL   SUMMARY. 

ENGLISH  EDITIONS. 

First  Edition:  April,  1903. 
Second  Edition:  August,  1907. 
Third  Edition:  August,  1910. 
Fourth  Edition:  August,  1913. 

EDITIONS  IN  OTHER  LANGUAGES. 
Original  Dutch:  Five  Editions. 
German:  Ten  Editions. 
Italian:  Two  Editions. 
French:  One  Edition. 
Russian:    Two  Editions. 
Polish:  One  Edition. 
Japanese:  One  Edition. 


THE    SCIENTIFIC    PRESS 

ROBERT   DRUMMOND   AND   COMPANY 

BROOKLYN.    N.    Y. 


- 


AUTHOR'S  PREFACE  TO  THE  FOURTH  EDITION. 


A  NOVEL  can  be  reprinted  unchanged  so  long  as  there  is  a 
public  to  buy  it;  but  even  with  an  interval  of  only  a  few  years 
between  successive  issues,  each  new  edition  of  a  text-book 
of  chemistry  needs  not  only  a  careful  revision,  but  also  the 
rewriting  of  some  of  its  chapters. 

It  has,  therefore,  been  impossible  to  avoid  making  many 
alterations  for  this  new  edition.  One  of  the  chief  features  is 
the  additional  space  allotted  to  the  applications  in  organic 
chemistry  of  physico-chemical  methods  such  as  refraction, 
absorption,  viscosity,  and  so  on.  The  importance  of  these 
properties  in  organic  chemical  research  is  steadily  increasing, 
and  I  think  it  necessary  to  mention  them  even  in  a  short  text- 
book of  this  description. 

The  section  on  tautomerism  has  been  entirely  rewritten; 
and  the  chapters  on  the  benzene  derivatives  have  been  com- 
pletely rearranged,  because  I  have  found  it  possible  to  treat 
this  subject  more  systematically  than  formerly. 

When  this  book  is  read  for  the  first  time,  the  matter  printed 
from  small  type  should  be  omitted,  as  it  contains  numerous  refer- 
ences to  subsequent  portions  of  the  text.  Such  references  are  in 
great  measure  avoided  in  the  part  printed  from  large  type. 

I  am  again  indebted  to  Dr.  JAMIESON  WALKER  for  the  care 
bestowed  by  him  on  the  revision,  a  task  made  difficult  by  the 
numerous  alterations  and  extensive  rearrangement. 

A.    F.    HOLLEMAN. 

AMSTERDAM,  July,  1913. 

ill 


AUTHOR'S   PREFACE  TO  THE  FIRST  EDITION. 


MOST  of  the  short  text-books  of  Organic  Chemistry  contain  a 
great  number  of  isolated  facts;  the  number  of  compounds  described 
in  them  is  so  considerable  as  to  confuse  the  beginner.  Moreover, 
the  theoretical  grounds  on  which  this  division  of  the  science  is 
based  are  often  kept  in  the  background;  for  example,  the  proofs 
given  of  the  constitutional  formulae  frequently  leave  much  to  be 
desired.  However  useful  these  books  may  be  for  reference,  they 
are  often  ill-suited  for  text-books,  as  many  students  have  learned 
from  their  own  experience. 

In  this  book  I  have  endeavoured  to  keep  the  number  of  uncon- 
nected facts  within  as  narrow  limits  as  possible,  and  to  give  promi- 
nence to  the  theory  underlying  the  subject.  For  this  reason,  a 
proof  of  the  structure  of  most  of  the  compounds  is  given.  This  was 
not  possible  for  the  higher  substitution-products  of  the  aromatic 
series,  so  that  the  methods  of  orientation  employed  in  it  are  de- 
scribed in  a  special  chapter. 

Physico-chemical  theories,  such  as  the  laws  of  equilibrium, 
ionization,  and  others,  are  becoming  more  and  more  prominent  in 
organic  chemistry.  I  have  attempted  in  many  instances  to  show 
how  useful  they  are  in  this  branch  of  the  science.  Such  important 
technical  processes  as  the  manufacture  of  alcohol,  cane-sugar,  etc., 
are  also  included.  The  book  is  essentially  a  text-book,  and  makes 
no  claim  to  be  a  "Beilstein  "  in  a  very  compressed  form. 

I  am  deeply  indebted  to  Dr.  A.  JAMIESON  WALKER  for  the  excel- 
lent way  in  which  he  has  carried  out  the  difficult  task  of  translating 
this  book  from  the  original  second  Dutch  edition  into  English. 
Lastly,  it  may  be  mentioned  that  it  has  also  -been  translated  into 
German,  the  second  edition  having  just  appeared,  and  that  an 
Italian  edition  is  in  preparation. 

A.  F.  HOLLEMAN. 

GRONINGEN,  NETHERLANDS,  November,  1902. 

iv 


EDITOR'S  PREFACE  TO  THE  FOURTH  EDITION. 


ABOUT  one-eighth  of  the  matter  included  in  the  fourth 
edition  is  new,  and  many  minor  alterations  have  also  been 
made.  I  have  again  to  thank  Professor  HOLLEMAN  for  devoting 
much  time  and  energy  to  this  work.  It  has  been  found  neces- 
sary to  renumber  the  paragraphs  from  §  17  onwards,  a  fact  to 
be  borne  in  mind  when  comparing  the  present  issue  with  previous 
editions. 

References  in  the  text  to  "  Inorganic  Chemistry  "  allude  to 
Professor  HOLLEMAN'S  "  Text-Book  of  Inorganic  Chemistry/' 
edited  by  Dr.  HERMOX  C.  COOPER,  and  published  by  Messrs. 
JOHN  WILEY  &  SONS,  Ixc.  The  "  Laboratory  Manual  "  referred 
to  is  Professor  HOLLEMAN'S  "  Laboratory  Manual  of  Organic 
Chemistry  for  Beginners/7  published  under  my  editorship  by 
Messrs.  JOHN  WILEY  &  Soxs,  Ixc.  This  work  constitutes  an 
appendix  to  the  text-book,  and  should  be  employed  as  a  guide 
to  laboratory  work  prior  to  the  systematic  course  of  preparations 
essential  to  progress  in  the  study  of  organic  chemistry. 

I  have  pleasure  in  acknowledging  my  indebtedness  to  corre- 
spondents who  have  drawn  my  attention  to  errors  in  the  text 
and  to  other  points  needing  revision,  and  thus  materially  assisted 
me  in  preparing  the  manuscript  for  the  press;  and  my  obliga- 
tion to  Messrs.  JOHX  WILEY  &  Soxs,  Ixc.,  for  the  care  bestowed 
by  them  on  the  preparation  of  the  book  for  publication. 

A.  JAMIESON  WALKER. 
DERBY,  ENGLAND,  July,  1913. 

v 


CONTENTS. 


Light  figures  refer  to  pages,  old  style  figures  to  paragraphs. 

PAGE 

INTRODUCTION  (1-27) 1 

Qualitative  and  quantitative  analysis  (3-9) 3 

Detection  of  the  elements,  3.  Estimation  of  carbon  and  hydrogen, 
5.  Estimation  of  nitrogen,  7.  Estimation  of  halogens,  sulphur, 
phosphorus,  and  other  elements,  8.  Calculation  of  formulae,  10. 

Determination  of  molecular  weight  (10-15) 11 

VICTOR  MEYER'S  method,  12.  Cryoscopic  methods,  14.  Ebullio- 
scopic  methods,  14. 

The  element  carbon  (16) 19 

Laboratory-methods  (17-26) 19 

Heating  substances  together,  19.  Distillation,  21.  Vacuum-  . 
distillation,  21.  Fractional  distillation,  22.  Steam-distillation, 
26.  Separation  of  two  immiscible  liquids,  28.  Separation  of 
solids  and  liquids,  30.  Separation  of  solids  from  one  another, 
30.  Determination  of  melting-points,  31.  Determination  of 
boiling-points,  31.  Determination  of  specific  gravity,  32. 
Polarimetry,  32.  Determination  of  refraction,  33.- 

Classification  of  organic  compounds  (27) 34 

FIRST  PART. 
ALIPHATIC  COMPOUNDS   (28-273) 35 

SATURATED  HYDROCARBONS  (28-38) 35 

Occurrence,  35.  Preparation,  35.  Physical  and  chemical  properties, 
36.  Nomenclature,  37.  Petroleum,  38.  Homologous  series,  40. 
Isomerism  and  structure,  42.  Carbon  chains,  45.  Law  of  the  even 
number  of  atoms,  46.  Number  of  possible  isomerides,  46.  Physi- 
cal properties  of  isomeric  compounds,  48. 

ALCOHOLS,  CnH2n+  2O  (39-50) 49 

Methods  of  formation  and  constitution,  49.  Nomenclature  and  iso- 
merism,  51.  General  properties  of  the  alcohols,  52.  Methyl  alco- 
hol, 53.  Ethyl  alcohol,  54.  Propyl  alcohols,  59.  Butyl  alcohols, 
60.  Amyl  alcohols,  62.  VAN  'T  HOFF'S  theory  of  stereoisomerism, 
64.  Higher  alcohols,  66.  Alkoxides,  66. 

ALKYL  HALIDES,  ESTERS,  AND  ETHERS  (51-56) otf 

Alkyl  halides,  69,    Esters  of  other  mineral  acids,  72.    Ethers,  74. 

vii 


vin  CONTENTS. 

PAGE 

ALKYL-RADICALS  LINKED  TO  SULPHUR  (57-60) 77 

Mercaptans,  78.     Thioethers,  79.     Sulphonic  acids,  80. 

ALKYL-RADICALS  LINKED  TO  NITROGEN  (61-70) 82 

Amines  (61-67) 82 

Nomenclature   and   isomerism,   83.     Methods  of  formation,   83. 
Properties,  86.     Individual  members,  87. 

Nitro-compounds  (68-70) 91 

Preparation,  91.     Properties,  92.     Derivatives,  93. 

ALKYL-RADICALS  LINKED  TO  OTHER  ELEMENTS  (71-75) 95 

Alkyl-radicals  linked  to  elements  of  the  nitrogen  group^i-^j^) 95 

Phosphines,  95.     Arsines,  96.     Stibines  and  Bismuthines,  97. 

Alkyl-radicals  linked  to  the  elements  of  the  carbon  group  (74) 97 

Optically  active  compounds  with  asymmetric  atoms  other  than 

carbon,  98. 
Metallic  alkides  (75) 100 

NlTRILES  AND  WoNlTRILES   (76-78) 102 

Carbylamines,  103.     Nitriles,  104. 

ACIDS,  CnH2nO2  (79-88) 105 

Constitution,  105.     Syntheses,  105.     General  properties,  107.    Formic 
acid,  109.     Acetic  acid,  110.     Butyric  acids,   113.     Higher  fatty 
acids,  114.     Soaps,  115.     Electrolytic  dissociation,  116. 
DERIVATIVES  ]  OF   THE    FATTY   ACIDS   OBTAINED    BY   MODIFYING   THE 

CARBOXYL-GROUP  (89-97) 119 

Acid  chlorides,   119:     Acid  anhydrides,   120.     Esters,   120.     Thio- 
>      acids  and  acid  amides,  127.     Other  derivatives,  128. 

ALDEHYDES  AND  KETONES  (98-111) 130 

General  properties  (98-193) 130 

Constitution,  130.  Nomenclature,  132.  Methods  of  forma- 
tion, 132.  Properties  common  to  both  classes,  133. 

Aldehydes  (104-109) 137 

Special  properties,  137.  Aldehyde-resin,  139.  Aldol-condensa- 
tion,  139.  Tests,  141.  Formaldehyde,  141.  Acetaldehyde, 
143.  Paracetaldehyde,  143.  Metacetaldehyde,  143. 

Ketones  (no,  in) 145 

Special  properties,  145.     Acetone,  146. 

TlNSATURATED  HYDROCARBONS  (l  12-127) 147 

Alkylenes  or  olefines,  CnH2n  (112-120) 147 

Methods  of  formation,-  147.  Properties,  148.  Ethylene,  150. 
Amylenes,  151.  The  nature  of  the  double  carbon  bond,  151. 

Alicyclic  compounds  (121) 157 

Hydrocarbons  with  triple  bonds,  CnH2n-2  (122-126) 158 

Nomenclature,  158.  Methods  of  formation,  158.  Properties. 
159.  Acetylene,  160. 

Hydrocarbons  with  two  double  bonds,  CnH2n-2  (127) x62 

Isoprene,  162.     Dimethylallene,  162.     Conjugated  system,  163. 


CONTENTS.  ix 


SUBSTITUTION-PRODUCTS    OP   THE  UNSATURATED  HYDROCARBONS  (128- 

i33) 164 

Unsaturated  halogen  compounds  (128-130) 164 

Preparation,  164.  Properties,  165.  Allyl  chloride,  165.  Vinyl 
chloride  and  bromide,  165.  Allyl  bromide  and  iodide,  166. 
Propargyl  compounds,  166.  Bromoacetylidene,  166. 

Unsaturated  alcohols  (131-133) 166 

Vinyl  alcohol,  167.  Neurine,  167.  Allyl  alcohol,  167.  Prop- 
argyl alcohol,  168. 

MONOBASIC  UNSATURATED  ACIDS  (134-140) 169 

Acids  of  the  olelc  series  (134-138) 169 

Preparation,  169.  Nomenclature,  169.  Properties,  170.  Acrylic 
acid,  170.  Acids  of  the  formula  C4H6O2,  171.  Oleic  acid,  172. 

Acids  of  the  propiolic  series  (139,  140) , . . . .   173 

Preparation,  173.     Properties,  174. 

UNSATURATED  ALDEHYDES  AND  KETONES  (141-143) 175 

Acraldehyde,  175.     Crotonaldehyde,  176.     Propiolaldehyde, 
176.     Geranial,  176.     Derivatives  of  geranial,  177. 

COMPOUNDS  CONTAINING  MORE  THAN  ONE  SUBSTITUENT  (144-160) 179 

Halogen  derivatives  of  methane  (144-146) 179 

Chloroform,  179.  Methylene  chloride,  181.  Tetrachloro- 
methane,  181.  Bromoform,  181.  lodoform,  181.  Methyl- 
ene iodide,  182. 

Halogen  derivatives  of  the.  homologues  of  methane  (147,  148) 182 

Preparation,      182.     Nomenclature,      183.     Tetrachloroethane, 
184.     Ethylene    chloride,    184.     Hexachloroethane,    184. 
Ethylene  bromide,  184.     Trimethylene  bromide,  184. 

Polyhydric  alcohols  (149-157) 185 

Glycols,  185.     Trihydric  alcohols,  188.     Tetrahydric  and  higher 

alcohols,  193. 
Derivatives  containing  halogen  atoms,  hydroxyl-groups,  nitro-groups, 

or  amino-groups  (158-160) 194 

Chloroethers,  195.  Halogen-hydrins,  195.  Dinitro-compounds, 
195.  Diamines,  196.  Choline,  196.  Lecithin,  197. 

POLYBASIC  ACIDS  (161-174) 198 

Saturated  diabasic  acids  (161-168) 198 

Physical  and  chemical  properties,  198.  Oxalic  acid,  200. 
Malonic  acid,  202.  Carbon  suboxide,  205.  Succinic  acid, 
205.  Electro-synthesis  of  dibasic  and  other  acids,  207. 
Formation  of  anhydrides,  208 . 

Unsaturated  dibasic  acids  (169-173) 210 

Fumaric  acid  and  malei'c  acid,  210.  Affinity-constants  of  the 
unsaturated  acids,  215.  Dibasic  acids  with  more  than  one 
triple  bond,  216. 

Higher  polybasic  acids  (174) 217 

Tricarballylic  acid,  217.     Aconitic  acid,  218. 


CONTENTS. 


SUBSTITUTED  ACIDS  (175-197) 219 

Halogen-substituted  acids  (175-178) 219 

Formation,  219.  Properties,  219.  Chloroacetic  acids,  221. 
Acids  with  more  than  one  halogen  atom  in  the  molecule,  221. 

Monobasic  hydroxy-acids  (179-186) 223 

Formation,  223.  Properties,  224.  Glycollic  acid,  226.  Hydroxy- 
propionic  acids,  226.  Lactones,  230. 

Dibasic  hydroxy-acids  (187-196) 232 

Tartronic  acid,  232.  Malic  acid,  232.  Tartaric  acids,  233. 
d-Tartaric  acid,  238.  Z-Tartaric  acid,  240.  r-Tartaric  acid, 
240.  Mesotartaric  acid,  241.  Racemic  substances,  and 
their  resolution  into  optically  active  constituents,  245. 

Polybasic  hydroxy-acids  (197) 248 

Citric  acid,  248. 
DlALDEHYDES  AND  DlKETONESI    HALOGEN-SUBSTITUTED  ALDEHYDES 

AND  KETONES  (198-201) 250 

Dialdehydes  (198) 250 

Glyoxal,  250.     Succindialdehyde,  251. 

Diketones  (199,  200) 251 

Diacetyl,  252.     Acetylacetone,  253.     Acetonylacetone,  25*4. 

Halogen-substituted  aldehydes  (201) 254 

Chloral,  254.     Chloral  hydrate,  254. 

ALDEHYDO-ALCOHOLS  AND  KETO-ALCOHOLS  OR  SUGARS  (202-228) 257 

Nomenclature  and  general  properties  of  the  monoses  and  their  derivatives 

(202,  203) ., 257 

Constitution  of  the  monoses  (204,  205) 259 

Methods  of  formation  of  the  monoses  (206) 262 

Monoses  (207-212) 264 

Pentoses,  264.     Hexoses,  266.     Stereochemistry,  273. 

Dioses  (213-223) 276 

Constitution,  276.  Maltose,  277.  Lactose,  278.  Sucrose, 
279.  Manufacture  of  sucrose  from  sugar-beet,  282.  Quan- 
titative estimation  of  sucrose,  283.  Velocity  of  inversion  of 
sucrose,  284.  Fermentation  and  the  action  of  enzymes,  285. 
Asymmetric  synthesis,  288. 

Polyoses  (224-228) 289 

Eaffinose,  289.  Starch,  291.  Glycogen,  294.  Manufacture 
of  starch,  294.  Cellulose,  294.  Technical  applications  of 
cellulose;  Nitrocelluloses;  Artificial  silk,  295. 

AMINO-ALDEHYDES  AND  AMINO-KETONES  (229) 298 

Aminoacetaldehyde,  298.     Muscarine,  298.     Chitin,  298. 

ALDEHYDO-ACIDS  AND  KETONIC  ACIDS  (230-239) 299 

Aldehydo-acids  (230) ; 299 

Glyoxylic  acid,  299. 

Ketonic  acids  (231-234) 300 

Pyroracemic   acid,  300.     Acetoacetic    acid,    301.     Acetoacetic- 


CONTENTS,  xi 

PAGE 

ester  synthesis,   302.     Lsevulic  acid,   304.     Mesoxalic  acid, 
305. 

Tautomerism  (235-237) 305 

Ethyl  acetoacetate,  305.     Oximes,  310. 

Pyrone  derivatives  (238,  239) 311 

Chelidonic  acid,  311.  Dimethylpyrone,  312.  Oxonium  salts,  314. 

AMINO-ACIDS  (240-245) 316 

Formation  (240) 316 

General  properties  (240,  241) 316 

Individual  members  (242,  243) 318 

Glycine,  318.  Betaine,  318.  Alanine,  319.  Leucine,  319. 
isoLeucine,  319.  Asparagine,  320.  Glutamine,  320.  Lysine, 
320.  Ornithine,  321. 

The  WALDEN  inversion  (244) 321 

Examples,  321.     WERNER'S  theory,  322. 

Ethyl  diazoacetate  (245) 323 

Formation,  323.     Properties,  323. 

PROTEINS  (246-254) 325 

Composition,  325.  Properties,  326.  Tests,  327.  Nomenclature, 
327.  Classification,  328.  Structure  of  the  molecule,  333.  Syn- 
thesis, 336.  Molecular  weight,  338. 

CYANOGEN  DERIVATIVES  (255-262) 340 

Cyanogen,  340.  Hydrocyanic  acid,  341.  Cyanides,  342.  Cyanic 
acid,  344.  Thiocyanic  acid,  346.  Fulminic  acid,  349.  Cyanuric 
acid  and  tsocyanuric  acid,  349. 

DERIVATIVES  OF  CARBONIC  ACID  (263-270) .- 351 

Carbonyl  chloride,  351.  Carbon  disulphide,  352.  Carbon  oxysul- 
phide,  353.  Urea,  353.  Derivatives  of  carbamic  acid,  358. 
Thiourea,  359.  Guanidine,  360. 

URIC-ACID  GROUP  (271-273) 362 

Parabanic  acid,  362.  Oxaluric  acid,  362,  Alloxan,  362.  Alloxantine, 
363.  Allantoine,  363.  Uric  acid,  364.  Purine,  365.  Xanthine,  366. 
Theobromine,  366.  Caffeine,  366.  Electro-reduction  of  purine  de- 
rivatives, 368. 

SECOND   PART. 

CYCLIC  COMPOUNDS  (274-416) 373 

INTRODUCTION  (274) \ 373 

Classification  of  cyclic  compounds 373 

A.    CARBOCYCLIC  COMPOUNDS  (275-386) 375 

1.  ALICYCLIC   COMPOUNDS  (275-280) 375 

q/doPropane    derivatives,    375.     q/cZoButane    derivatives,    375. 
q/cfoPentane  derivatives,  376.     Higher  alicyclic  derivatives,  378. 

2.  AROMATIC    COMPOUNDS  (281-386) .380 


xii  CONTENTS. 

PAGE 

CONSTITUTION  OF  BENZENE  (281-284) 380 

Relation  to  the  aromatic  compounds,  380.  Structure  of  the  mole- 
cule, 381.  Formulae  of  KEKULE  and  THIELE,  384.  Nomenclature 
and  isomerism  of  the  benzene  derivatives,  384. 

PROPERTIES  CHARACTERISTIC  OF  THE  AROMATIC  COMPOUNDS:  SYNTHESES 

FROM  ALIPHATIC  COMPOUNDS  (285) 386 

BENZENE  AND  THE  AROMATIC  HYDROCARBONS  WITH  SATURATED  SIDE- 
CHAINS  (286-288) 388 

Gas-manufacture  and  its  by-products:  Tar,  388.  Benzene  and  its 
homologues,  389. 

MONOSUBSTITUTION-PRODUCTS        OF       THE       AROMATIC       HYDROCARBONS 

(289-320) 393 

Monohalogen  compounds  (289) 393 

Mononitro-derivatives  (290) 395 

Preparation,  395.     Nitrobenzene,  395.     Nitrotoluenes,  396. 

Monosulphonic  adds  (291) 397 

Formation,  397.  Properties,  397.  Sulphonyl  chlorides,  397. 
Sulphonamides,  398. 

Monohydric  phenols  (292-295) 398 

Formation,  398.  Properties,  399.  Phenol,  400.  Cresols,  400. 
Thymol,  400.  Ethers,  400. 

Monoamino-compounds  (296-299*) 401 

Formation,  401.     Properties,  401.     Aniline,  403.     Homologues 
of  aniline,  404.     Secondary  amines,  404.     Tertiary  amines, 
405.     Quaternary  bases,  407. 
Intermediate  products  in  the  reduction  of  aromatic  nitro-compounds 

(300-304) 407 

Azoxybenzene,    408.     Azobenzene,    408.     Hydrazobenzene, 
409.     Benzidine,  409.     Electro-reduction  of  nitro-com- 
pounds, 409. 

Diazo-compounds  (305-309) 413 

Classification,  413.  Constitution  of  the  diazonium  salts,  414. 
Reactions  of  the  diazonium  compounds,  415.  Diazoamino- 
compounds,  419.  Aminoazo-compounds,  419.  Hydroxyazo- 
compounds,  420. 

Hydrazines  (310) 420 

Phenylhydrazine,  420.     Methylphenylhydrazine,  421. 
Aromatic  monobasic  acids:  Benzole  add  and  its  homologues  (311-313)..    421 
Formation,  422.     Benzole  acid,  423.     Benzoyl  chloride,  424. 
Benzole  anhydride,  425.     Ethyl  benzoate,  425.     Benzamide, 
425.     Benzonitrile,  426.     Toluic  acids,  426.     Xylic  acids,  426. 

Aromatic  aldehydes  and  ketones  (314-318) 426 

Aldehydes,  426.  Autoxidation,  428.  Ketones,  429.  Oximes, 
431. 

Aromatic  phosphorus  and  arsenic  derivatives  (319) 433 

Phosphinobenzene,  433.     Phenylphosphinic  acid,  434.     Phenyl- 


CONTENTS.  xiu 

PAGE 

phosphine,  434.     Phosphenyl  chloride,  434.     Phosphobenzene, 
434.     Phosphenylous  acid,  434.     Arsinobenzene,  434.    Phenyl- 
arsinic  acid,  434.     Arsenobenzene,  434.     Phenylarsine  oxide, 
434. 
Aromatic  metallic  compounds  (320) 435 

BENZENE  HOMOLOGUES  WITH  SUBSTITUTED  SIDE-CHAINS  (321-326) 436 

Compounds  with  halogen  in  the  side-chain  (321) 436 

Formation,  436.  Benzyl  chloride,  437.  Benzyl  bromide,  437. 
Benzyl  iodide,  437.  Benzal  chloride,  438.  Benzotrichloride, 
438. 

Phenylnitromethane  and  the  pseudoac^ds  (322,  323) 438 

Acids  with  carboxyl  in  the  side-chain  (324) 440 

Phenylacetic  acid,  440.     Mandelic  acid,  440. 

Aromatic  alcohols  (325) 441 

Benzyl  alcohol,  441. 

Compounds  with  the  amino-group  in  the  side-chain  (326) 441 

Benzylamine,  441.     Dibenzylamine,  441.     Tribenzylamine,  441. 

COMPOUNDS  CONTAINING  AN  UNSATURATED  SIDE-CHAIN  (327,  328) 443 

Hydrocarbons  (327) 443 

Styrole,  443.     Phenylacetylene,  443. 

Alcohols  and  aldehydes  (327) 443 

Cinnamyl  alcohol,  443.     Cinnamaldehyde,  444. 

Acids  (328) 443 

Cinnamic  acid,  444.  Allocmusunic  acid,  445.  isoCinnamic 
acids,  445. 

POLYSUBSTITUTED  BENZENE  DERIVATIVES  (329-353) 446 

Polyhalogen  derivatives  (329) 446 

Halogen-nitro-compounds  (330) 447 

Polynitro-derivatives  (331) 448 

Dinitrobenzenes,  448.  Trinitrobenzenes,  448.  Trinitrobutyl- 
xylene,  449. 

Substituted  benzenesulphonic  acids  (332) 449 

Substituted  phenols  and  polyhydric  phenols  (333-338) 450 

Halogenphenols,  450.  Nitrophenols,  450.  Phenolsulphonic 
acids,  452.  Nitrosophenol,  453.  Dihydric  phenols,  453. 
Trihydric  phenols,  455.  Higher  phenols,  457.  Quinones,  457. 

Substitution-products  of  aniline  (339-341) 459 

Nitroanilines,  459.  p-Aminobenzenesulphonic  acid,  460.  Ammo- 
phenols,  461.     Polyamino-compounds,  462.     Azo-dyes,  464. 
\    Substituted  benzole  acids;    Polybasic  acids  and  their  derivatives  (342- 

350) 468 

Halogenbenzo'ic  acids,  468.  Nitrobenzo'ic  acids,  469.  Sulpho- 
benzoic  acids,  469.  Monohydroxy-acids,  470.  Xanthone- 
dyes,472.  Flavone-dyes,  472.  Dihydroxy-acids,  472.  Trihy- 
droxy-acids,  473.  Aminobenzoic  acids,  475.  Phthalic  acid, 


xiv  CONTENTS. 

PAGE 

476.    isoPhthalic  and  Terephthalic  acids,  480.     Higher  poly- 
basic  acids,  481. 

Substituted  aldehydes  (351) 481 

Nitrobenzaldehydes,  481.     Hydroxyaldehydes,  481. 
Polysubstituted  benzene  derivatives  with  substituents  in  the  side-chain 

(352,  353) 483 

p-Hydroxyphenylpropionic  acid,  483.  o-Hydroxycinnamic  acid, 
483.  Coumarin,  484.  Piperic  acid,  484.  Piperonal,  484. 
Adrenaline,  485.  Hordenine,  486.  p-Hydroxyphenylthyl- 
amine,  486. 

ORIENTATION  OF  AROMATIC  COMPOUNDS  (354-362) 487 

General  principles,  487.  Absolute  determination  of  position  for 
ortho-compounds,  488.  Absolute  determination  of  position  for 
r/ieia-compounds,  490.  Absolute  determination  of  position  for 
para-compounds,  492.  Determination  of  position  for  the  trisub- 
stituted  and  higher-substituted  derivatives,  493.  Equivalence 
of  the  six  hydrogen  atoms  in  benzene,  495.  Influence  of  the  sub- 
stituents on  each  other,  496 . 

HYDROCYCLIC  OR  HYDROAROMATIC  COMPOUNDS  (363-370) 503 

Hydrocyclic  compounds  (363,  364) 503 

Preparation,  503.  q/cfoHexane,  505.  p-Diketoq/cfohexane,  506. 
Quinitols,  506.  Inositol,  507.  q/c/oHexanone,  507.  Hydro- 
cyclic  acids,  507. 

Terpenes  (365-369) 508 

Isolation,  508.  Nomenclature,  508.  Menthol,  508.  Terpin, 
509.  Terpineol,  512.  Pulegone,  513.  Terpinolene,  513. 
Limonenes,  514.  Carvone,  514.  Carvacrol,  514.  Polycyclic 
terpene  derivatives,  516. 

Camphors  (370) 518 

Camphor,  518.  Borneol,  518.  Camphoric  acid,  519.  Cam- 
phoronic  acid,  519.  Synthesis  of  camphor,  520.  Camphane, 
520.  Thujone,  521. 

Polyterpenes  (370) 521 

Caoutchouc,  521.     1 :  5-Dimethylq/c£ooctadiene,  522. 
BENZENE-NUCLEI    LINKED    TOGETHER    DIRECTLY    OR    INDIRECTLY    BY 

CARBON  (371-376) 523 

Diphenyl  (371) 523 

Diphenylmethane  (372) 524 

Triphenylmethane  and  its  derivatives  (373-375) 525 

Triphenylmethane,  525.  Leucomalachite-green,  526.  Mala- 
chite-green, 526.  Quinonoid  reaction,  526.  Halochromy, 

527.  Stages  in  the  formation  of  the  triphenylmethane  dyes, 

528.  Crystal-violet,  528.     Pararosaniline,  529.     Paraleucan- 
iline,  529.     Rosaniline,  529.     Magenta,  530.     Methyl-violet, 
530.     Aniline-blue,     530.     Rosolic     acid,     530.     Triphenyl- 

J:   -    methyl,  531. 


CONTENTS.  xv 

PAGE 

Dibenzyl  and  its  derivatives  (376) 532 

Dibenzyl,  532.  Stilbene,  532.  Benzoin,  533.  Hydrobenzoin, 
533.  Benzil,  533.  Benzilic  acid.  533. 

CONDENSED  BENZENE-NUCLEI  (377-386) 534 

Naphthalene  (377-381) 534 

Preparation  from  coal-tar,  534.  Properties,  534.  Constitu- 
tion, 535.  Number  of  substitution-products,  536.  Orienta- 
tion, 537.  Substitution-products,  538.  Addition-products, 
541. 

Anthracene  (382-385) 544 

Preparation  from  coal-tar,  544.  Properties,  544.  Constitu- 
tion, 544.  Number  of  substitution-products,  545.  Orienta- 
tion, 545.  Anthraquinone,  545.  Anthraquinol,  547.  Oxan- 
throne,  547.  Anthrone,  548.  Anthranol,  548.  Alizarin, 
548.  Lakes,  550.  Purpurin,  550.  Indanthren-group,  551. 

Phenanthrene  (386) 551 

Preparation  from  anthracene-oil,  551.  Properties,  551.  Con- 
stitution, 551.  Phenanthraquinone,  552.  Dimethylmorphol, 
553. 

B.    HETEROCYCLIC  COMPOUNDS  (387-416) 554 

NUCLEI  CONTAINING  NITROGEN,  OXYGEN,  AND  SULPHUR  (387-399) 554 

Pyridine  (387-391) 554 

Preparation  from  coal-tar,  554.  Properties,  554.  Constitu- 
tion, 555.  Number  of  substitution-products,  556.  Orienta- 
tion, 556.  Homologues,  557.  a-Propenylpyridine,  558. 
Piperidine,  559.  Piperine,  559.  Piperic  acid,  559.  Pyridine- 
carboxylic  acids,  559. 

Furan  (392,  393) 561 

Constitution,  561.  Preparation  of  derivatives,  561.  Furfur- 
aldehyde,  562.  Furfuramide,  562.  Furfuro'in,  562.  Hydroxy- 
methylfurfuraldehyde,  563.  Dehydromucic  acid,  563.  Pyro- 
mucic  acid,  563. 

Pyrrole  (394,  395) 564 

Preparation,  564.  Properties,  564.  Synthesis,  564.  Constitu- 
tion, 565.  Derivatives,  565. 

Thiophen  (396,  397). . 566 

Preparation,  566.  Synthesis,  567.  Properties,  567.  Homo- 
logues, 567.  Derivatives,  568. 

Pyrazole  (398,  399) 568 

Formation  of  derivatives,  568.  Synthesis  and  constitution, 
569.  Identity  of  derivatives  with  substituents  at  positions 
3  and  5,  569.  Pyrazoline,  570.  Pyrazolone,  570.  Methyl- 
phenylpyrazolone,  570.  "  Antipyrine,"  570.  "  Salipyrine," 
571. 


xvi  CONTENTS. 

PAGE 

CONDENSATION-PRODUCTS  OF  BENZENE  AND  HETEROCYCLIC  NUCLEI  (400- 

405) 572 

Quinoline  (400,  401) 572 

Properties,  572.  Synthesis,  572.  Constitution,  573.  Orienta- 
tion, 573.  Nomenclature,  574.  Derivatives,  574. 

isoQuinoline  (402) 575 

Properties,  575.     Constitution  and  synthesis,  575. 

Indole  (403-405) 575 

Relation  to  indigo,  575.  Constitution,  576.  Scatole,  577. 
Tryptophan,  577.  3-Indolealdehyde,  577.  Indigo,  578. 
Indoxyl,578.  Indigo-white,  580.  Vat-dyestuffs,  580.  Indig- 
oids,  581.  "  Purple  of  the  ancients,"  581.  Thioindigo,  581. 

ALKALOIDS  (406-416) 582 

Classification  (406) 582 

Properties  (407) 582 

Extraction  from  plants  (408) 583 

Individual  alkaloids  (409-416) 583 

Coniine,  583.     Nicotine,  584.     Atropine,  584.     Cocaine,  586. 
Morphine,  586.    Heroin,  588.    Narcotine,  588.    Nornarcotine, 
588.       Cotarnine,  588.       Quinine,  589.       Cinchonine,  589.  j 
Strychnine,  590,     Brucine,  590.     Curarine,  590. 

INDEX.  .  591 


FIGURES. 


FIRST   PART. 

FIGURE  PAGB 

1 .  Organic  analysis 5 

2.  Potash-bulbs 6 

3.  Tube-furnace 9 

4.  VICTOR  MEYER'S  vapour-density  apparatus 12 

5.  EYKMAN'S  graphic  method 15 

6.  EYKMAN'S  depressimeter 17 

7.  EYKMAN'S  boiling-point  apparatus 17 

8.  Heating  substances  in  an  open  flask 20 

9.  Flask  with  reflux-condenser 20 

10.  Distillation-apparatus 21 

11.  Fractionating-flask v. 21 

12.  Distillation  in  vacuum 22 

13.  Fractionating-columns 23 

14.  15,  16.  Fractional-distillation  curves 25 

17.  Steam-distillation 27 

18.  Separating-funnel 28 

19.  Filtering-flask 30 

20.  THIELE'S  melting-point  apparatus 31 

21.  Pyknometer 32 

22.  LAURENT'S  polarimeter 33 

23.  Fractionating-column 55 

24.  Carbon  tetrahedron 65 

25.  26.  Asymmetric  C-atoms 65 

27.  Solubility-curves  for  triethylamine  and  water 89 

28.  Usual  form  of  solubility-curve  for  two  liquids 89 

29.  Asymmetric  molecular  structure 99 

30.  Melting-point  curve  of  the  fatty  acids 107 

31.  Preparation  of  vinegar  by  the  "  quick  "  or  German  process 110 

32.  Graphic  representation  of  the  melting-points  of  the  acids  CnH2n-2O4.  199 

33.  Spacial  representation  of  the  bonds  between  2-5  C-atoms 208 

34.  35.  Single  bond  between  two  carbon  atoms 211 

36,  37,  38.  Graphic  spacial  representation  of  the  double  bond  between 

two  carbon  atoms 211 

39.  Fumaric  acid ,  ,  , 213 

xvii 


xviii  FIGURES. 

FIGURE  PAG8 

40.  Dibromosuccinic  acid 213 

41.  Maleic  acid 213 

42.  tsoDibromosuccinic  acid 213 

43.  Dibromosuccinic  acid 214 

44.  Bromomaleiic  acid 214 

45.  tsoDibromosuccinic  acid 214 

46.  Bromofumaric  acid 214 

47.  Erucic  acid 222 

48.  49.  Dibromoerucic  acid 222 

50.  Brassidic  acid 223 

51,  52.  Dibromobrassidic  acid 223 

53.  Acetaldehyde 228 

54,  55.  Lactonitrile t 228 

56,  57.  Conversion  of  an  optically  active  substance  into  its  optical  iso- 

meride 229 

58,  59.  EMIL  FISCHER'S  spacial  representation  of  two  C-atoms  in  union. .  235 

60.  Electrolysis  of  an  alkaline  copper  solution 239 

61.  Maleic  acid 242 

62,,  63.  Mesotartaric  acid 242 

64.  Fumaric  acid 243 

65.  Racemic  acid 243 

66.  Crystal  forms  of  the  sodium  ammonium  tartrates 246 

67.  Rye-starch 292 

68.  Rice-starch \ 292 

69.  Potato-starch - 293 

70.  WERNER'S  theory  of  the  WALDEN  Inversion 322 

71.  Normal  reduction-curve '. 370 

72.  Abnormal  reduction-curve .  .                                                                     .  370 


SECOND  PART. 

73.  KEKULE'S  benzene-formula 384 

74.  THIELE'S  benzene-formula 384 

75.  Fusion-curve  of  mixtures  of  o-nitrotoluene  and  p-nitro toluene 396 

76.  HABER'S  electro-reduction  scheme .' .  412 

77.  Solubility-curve  of  benzole  acid  in  water 424 

78.  Enantiotropic  substance 430 

79.  Monotropic  substance 430 

80.  Centric  naphthalene-formula 536 

81.  THIELE'S  naphthalene-formula .  53t> 

82.  Simple  naphthalene-formula 536 


ORGANIC   CHEMISTRY. 


INTRODUCTION. 

i.  Organic  Chemistry  is  the  Chemistry  of  the  Carbon  Com- 
pounds. The  word  " organic"  has  now  lost  its  historic  meaning, 
given  it  at  a  time — the  beginning  of  last  century — when  it  was 
thought  that  the  substances  which  occur  in  organized  nature,  in 
the  animal  and  vegetable  kingdoms,  could  only  be  formed  under 
the  influence  of  a  special,  obscure  force,  called  the  vital  force. 
Several  unsuccessful  attempts  to  prepare  artificially  such  "  or- 
ganic" substances  promoted  this  belief.  Until  about  the  year 
1840,  it  was  so  general  that  BERZELIUS  still  thought  that  there 
was  but  little  hope  of  ever  discovering  the  cause  of  the  difference 
between  the  behaviour  of  the  elements  in  the  mineral  kingdom 
and  in  living  bodies.  Organic  chemistry  included  the  study  of 
those  compounds  which  occur  in  plants  and  animals,  as  well  as  of 
the  more  or  less  complicated  decomposition-products  which  could 
be  prepared  from  these  compounds  by  various  means.  Among 
the  latter  many  were  known  which  were  not  found  in  nature,  but 
it  was  thought  impossible  to  build  up  a  compound  body  from  its 
decomposition-products,  or  to  obtain  an  organic  compound  from 
its  elements. 

In  the  year  1828,  WOHLER  had  indeed  obtained  from  inorganic 
sources  the  organic  compound  urea,  a  product  of  the  animal 
economy.  This  discovery  was  at  first  regarded  as  of  small  im- 
portance, for  it  was  thought  that  this  substance  occupied  a  position 
midway  between  organic  and  inorganic  compounds.  For  a  num- 
ber of  years  the  synthesis  of  urea  was  in  fact  the  only  well-known 
example  of  the  kind,  such  observations  becoming  more  numerous 


2  ORGANIC  CHEMISTRY.  [§  2 

about  the  middle  of  the  nineteenth  century.  At  length  the  syn- 
thesis of  many  substances,  including  that  of  acetic  acid  by  KOLBB 
and  of  the  fats  by  BERTHELOT,  strengthened  the  growing  convic- 
tion that  organic  compounds  are  formed  under  the  influence  of  the 
same  forces  as  are  inorganic,  and  that  to  this  end  no  special  force 
is  necessary. 

The  natural  distinction  between  organic  and  inorganic  chem- 
istry was  thus  destroyed,  its  place  being  taken  by  an  artificial  one. 
As  it  had  been  already  noticed  that  all  organic  compounds  contain 
carbon,  the  name  " Organic  Chemistry"  was  appropriated  to  the 
Chemistry  of  the  Carbon  Compounds. 

Through  the  numerous  discoveries  which  were  made  in  this 
branch  of  the  science,  especially  in  Germany  by  LIEBIG,  WOHLER, 
and  their  pupils,  and  in  France  by  DUMAS,  LAURENT,  and  GER- 
HARDT,  organic  chemistry  acquired  by  degrees  a  totally  different 
aspect,  and  the  old  division  into  groups  of  substances  which  had 
either  the  same  origin,  as  in  the  case  of  vegetable  chemistry  or 
animal  chemistry,  or  had  single  properties  in  common,  as,  for 
example,  the  vegetable  acids,  the  vegetable  bases,  and  neutral 
vegetable  bodies,  vanished.  Its  place  was  taken  by  a  more  rational 
classification,  which  gradually  developed  into  its  present  form,  and 
is  based  on  the  mutual  relationships  found  to  exist  between  organic 
compounds. 

2.  Since  no  essential  distinction  between  organic  and  inorganic 
chemistry  now  exists,  and  numerous  syntheses  have  set  at  rest 
all  doubt  as  to  the  theoretical  possibility  of  building  up  from 
their  elements  even  the  most  complicated  carbon  compounds, 
such  as  the  proteins,  the  question  may  arise  as  to  the  reason 
for  still  treating  the  chemistry  of  the  carbon  compounds  as  a 
special  part  of  the  science.  The  answer  to  this  question  is  two- 
fold. 

First,  the  enormous  number  of  carbon  compounds  known, 
amounting  to  about  one  hundred  and  fifty  thousand,  the  number 
of  the  compounds  of  all  the  other  elements  being  only  about 
twenty-five  thousand.  Second,  the  special  nature  of  certain 
properties  of  the  carbon  compounds.  These  are  either  not  found 
at  all  in  the  compounds  of  other  elements,  or  at  most  in  a  much 
less  marked  degree:  for  example,  many  inorganic  compounds 
can  be  exposed  to  high  temperatures  without  undergoing  any 


§  3]  QUALITATIVE  ANALYSIS.  3 

chemical  change,  whereas  the  carbon  compounds,  almost  with- 
out exception,  are  decomposed  at  a  red  heat.  It  follows  that 
the  latter  are  usually  much  less  stable  than  the  former  towards 
chemical  and  physical  reagents,  and  in  consequence  different 
methods  are  employed  in  the  investigation  of  carbon  compounds 
and  of  inorganic  compounds. 

Another  peculiarity  is  that  numerous  organic  compounds  con- 
tain the  same  elements  in  the  same  proportions,  but  differ  from 
one  another  in  properties.  For  example,  one  hundred  and 
thirty-five  compounds  of  the  formula  CioHiaOaX  have  been 
discovered.  This  phenomenon  is  called  isomerism,  and  is  almost 
unknown  in  inorganic  chemistry,  a  fact  which  necessitates  an 
investigation  of  the  cause  to  which  it  is  due. 

All  these  reasons  make  it  desirable  to  treat  the  carbon  com- 
pounds in  a  special  part  of  chemistry. 


QUALITATIVE   AND   QUANTITATIVE    ANALYSIS. 

3.  Investigation  has  shown  that  in  most  of  the  compounds 
of  carbon  there  is  only  a  very  small  number  of  elements.  The 
chief  of  these  are  carbon,  hydrogen,  oxygen,  and  nitrogen.  Halogen 
derivatives  are  less  numerous,  and  substances  containing  sulphur 
or  phosphorus  occur  still  less  frequently.  Carbon  compounds  are 
also  known  in  which  other  elements  are  found,  but  they  are  ex- 
ceedingly few  in  comparison  with  those  which  contain  only  the 
elements  named  above.  Some  elements  do  not  occur  in  carbon 
compounds. 

In  order  to  be  able  to  determine  the  nature  of  a  compound,  it 
is  first  of  all  necessary  to  ascertain  what  elements  it  contains  by 
submitting  it  to  qualitative  analysis.  In  the  case  of  the  carbon 
compounds,  this  is  very  simple  in  theory,  the  process  being  one  of 
oxidation. 

On  solution  of  an  organic  compound,  the  elements  constituting 
it  are  usually  not  present  as  ions  in  the  liquid.  Oxidation,  however, 
either  converts  them  at  once  into  ions,  or  into  oxygen  compounds 
with  ionized  groups,  such  as  CO3",  SO4",  and  so  on.  They  can 
then  be  identified  by  the  ordinary  inorganic  reactions  ("Laboratory 
Manual,"  I,  1-5). 

Carbon  is  thus  converted  into  carbon  dioxide,  which  can  be 


ORGANIC  CHEMISTRY.  [§  4 

detected  by  the  lime-water  test;  sulphur  and  phosphorus  are 
oxidized  to  sulphuric  acid  and  phosphoric  acid  respectively;  hydro- 
gen is  oxidized  to  water;  and  nitrogen  is  evolved  in  the  free  state. 

If  an  organic  compound  contains  a  halogen,  it  is  oxidized  in 
presence  of  silver  nitrate,  the  corresponding  silver  halide  being 
formed.  Other  elements  present  are  found,  after  oxidation,  in 
the  form  of  compounds  easily  identified. 

For  analytical  purposes,  oxidation  is  carried  out  in  different 
ways,  according  to  the  nature  of  the  element  suspected  to  be 
present.  Copper  oxide  is  generally  used  in  testing  for  carbon, 
hydrogen,  and  nitrogen.  The  substance  is  mixed  with  it,  and 
the  mixture  heated  in  a  glass  tube  sealed  at  one  end,  the  carbon 
and  hydrogen  being  oxidized  by  the  action  of  the  oxygen  of  the 
copper  oxide.  Nitrogen  is  evolved  in  the  free  state,  and  can  be 
recognized  in  exactly  the  same  way  as  in  the  quantitative  analysis 
of  nitrogen  (7).  For  the  halogens,  sulphur,  phosphorus,  etc., 
it  is  best  to  oxidize  the  substance  under  examination  with  con- 
centrated nitric  acid. 

The  method  of  oxidation  is  a  general  one  for  qualitative  analy- 
sis: it  can  always  be  applied,  and  yields  positive  results.  There 
are  other  methods  which  in  many  cases  attain  the  desired  end 
more  quickly  and  easily,  but  as  most  of  these  are  not  of  universal 
application,  the  failure  of  one  of  them  to  detect  an  element  affords 
no  certain  indication  of  its  absence.  In  doubtful  instances  the 
question  must  be  decided  by  the  oxidation-process. 

For  example,  the  presence  of  carbon  can  frequently  be  de- 
tected by  submitting  the  substance  to  dry  distillation.  Charring 
often  takes  place,  or  vapours  are  evolved  which  can  be  recognized 
as  carbon  compounds  by  their  smell  or  other  properties,  such  as 
their  burning  with  a  smoky  flame  on  ignition. 

4.  The  nitrogen  in  many  organic  compounds  can  be  converted 
into  ammonia  by  heating  them  with  soda-lime,  or  with  concen- 
trated sulphuric  acid.  Another  method  very  largely  used  in  testing 
for  this  element  was  suggested  by  LASSAIGNE.  It  consists  in  heating 
the  substance  under  examination  with  a  small  piece  of  sodium  (or 
potassium)  in  a  narrow  tube  sealed  at  one  end.  Should  the  com- 
pound contain  nitrogen,  sodium  (or  potassium)  cyanide  is  formed, 
its  presence  being  readily  recognized  by  converting  it  into  Prussian 
blue  ("Laboratory  Manual,"  I,  3,  a). 


§§  5,  61 


QUANTITATIVE  ANALYSIS. 


5.  The  halogens  can  be  recognized  by  heating  the  substance 
with  quicklime,  the  corresponding  calcium  halide  being  formed. 
A  very  delicate  method  of  detecting  them  is  to  introduce  a  small 
quantity  of  the  compound  on  a  piece  of  copper  oxide  into  a  non- 
luminous  flame.     The  corresponding  copper  halide  is  formed  and 
volatilizes,   imparting  a  magnificent  green   colour   to   the   flame. 
These  two  methods  are  always  applicable. 

Sulphur  can  often  be  detected  by  heating  the  compound  with 
a  small  piece  of  sodium  in  a  narrow  ignition-tube.  Sodium  sul- 
phide is  produced,  and  can  be  detected  by  treating  the  reaction- 
mixture,  placed  on  a  clean  silver  coin,  with  water,  when  a  black 
stain  of  silver  sulphide  is  formed.  Or,  the  reaction-mixture  can 
be  extracted  with  water,  and  sodium  nitroprusside  added:  the 
solution  acquires  an  intense  violet  colour. 

No  qualitative  reaction  is  known  for  detecting  oxygen  in  an 
organic  compound.  This  can  only  be  effected  by  a  quantitative 
analysis. 

6.  Following  on  qualitative,  must  come  quantitative,  analysis; 
that  is,  the  determination  of  the  quantity  of  each  element  present 
in  the  compound.     The  methods  used  for  qualitative  analysis  in 
inorganic  chemistry  are  often  very  different  from  those  employed 
in  quantitative  determinations:  in  organic  chemistry  the  methods 
of  qualitative  and  quantitative  analysis  are   alike   in  principle, 
oxidation  being  employed  in  both. 

Carbon  and  hydrogen  are  always  estimated  together.  The 
principle  of  the  method  of  organic  analysis  chiefly  used  was  worked 
out  by  LIEBIG  (1803-1873).  It  is  usually  carried  out  as  follows. 
In  the  combustion-furnace,  k  (Fig.  1),  is  a  hard  glass  tube,  abf 


FIG.  1. — ORGANIC  ANALYSIS. 

open  at  both  ends.     A  complete  drawing  of  it  is  shown  in  the 
figure  above  the  furnace.     It  contains  granulated  copper  oxide, 


6  ORGANIC  CHEMISTRY.  [§  6 

//,  and  a  spiral  of  copper-gauze,  c,  oxidized  by  heating  to  redness 
in  the  air  or  in  a  stream  of  oxygen.  About  one-third  of  the  length 
of  the  tube  is  left  empty,  and  into  this,  after  temporary  removal 
of  the  copper  spiral,  a  platinum  or  porcelain  boat,  d,  containing  a 
weighed  quantity  of  the  substance  to  be  analyzed,  is  introduced. 
The  end  of  the  tube  next  the  boat  is  connected  with  a  drying 
apparatus,  g,  h,  /,  in  which  the  air  or  oxygen  is  freed  from  water- 
vapour  and  carbon  dioxide:  g  contains  concentrated  caustic  potash, 
h  soda-lime,  and  /  calcium  chloride.  To  the  end  of  the  tube 
furthest  from  the  boat  is  attached  a  weighed  calcium-chloride  tube,  I, 
for  the  purpose  of  collecting  the  water  produced  by  the  combustion 

of  the  substance.'  The  weighed 
potash-bulbs,  m  (shown  enlarged  in 
Fig.  2),  are  connected  to  this,  and  in 
them  the  carbon  dioxide  formed  is 
absorbed  by  concentrated  caustic 
potash.  The  gases  enter  the  appara- 
tus by  the  tube  b  on  the  right,  pass 

FlG>  2.— P^ISH-BULBS.         through  the  three  bulbs   containing 

potash,  and  escape  through  the  tube 

a,  which  is  filled  with  soda-lime.  As  soon  as  all  the  joints  of  the 
apparatus  are  known  to  be  gas-tight,  the  burners  are  lighted,  except 
beneath  the  place  where  the  boat  is.  When  the  tube  is  hot,  the 
substance  is  burned  by  carefully  heating  this  part  of  the  tube, 
while  at  first  a  slow  stream  of  air,  and  later  a  slow  stream  of  oxy- 
gen, is  led  through  the  drying  apparatus  into  the  tube.  The 
oxygen  facilitates  the  combustion  of  the  particles  of  carbon  which 
have  deposited,  and  the  red-hot  copper  oxide  serves  to  oxidize 
the  gaseous  decomposition-products  completely  to  carbon  dioxide 
and  water.  The  increase  in  weight  of  the  calcium-chloride  tube 
and  that  of  the  potash-bulbs  respectively  give  the  quantity  of  water 
and  carbon  dioxide  formed,  from  which  the  amount  of  hydrogen 
and  carbon  in  the  compound  can  be  calculated. 

If  the  compound  contains  nitrogen  or  halogens,  a  freshly- 
reduced  spiral  of  copper-gauze  is  placed  at  the  end  of  the  tube 
next  the  absorption-apparatus  I  and  m.  The  hot  copper  decom- 
poses any  nitrogen  oxides  formed,  which  would  otherwise  be 
absorbed  in  the  potash-bulbs:  it  also  combines  with  and  retains 
the  halogens. 


§7J  QUANTITATIVE  ANALYSIS.  7 

The  foregoing  is  only  intended  to  illustrate  the  principles  on 
which  the  methods  of  organic  analysis  are  based.  The  experimental 
details  have  often  to  be  modified  somewhat  to  suit  special  circum- 
stances. For  example,  substances  which  burn  with  great  difficulty 
are  mixed  with  lead  chromate  instead  of  copper  oxide,  the  former 
being  the  more  energetic  oxidizing  agent.  When  the  compound  con- 
tains sulphur,  this  substance  is  also  used,  the  sulphur  being  con- 
verted, by  heating  in  contact  with  the  chromate,  into  lead  sulphate, 
which  is  stable  at  red  heat.  If  copper  oxide  is  used,  sulphur  dioxide 
is  formed  and  is  absorbed  in  the  potash-bulbs,  thereby  introducing 
an  error  into  the  carbon  estimation.  Another  method  of  retaining 
sulphur  dioxide  consists  in  having  a  layer  of  lead  dioxide,  Pb02,  at 
the  end  of  the  tube  next  to  the  absorption-apparatus.  This  layer 
is  gently  heated,  and  retains  all  the  sulphur  dioxide  in  the  form  of 
lead  sulphate.  Combustion  tubes  of  silica  are  also  employed,  and 
are  superior  to  glass  in  their  power  of  resisting  fracture.  Contact  of 
the  copper  oxide  with  the  inner  surface  of  the  tube  should  be  pre- 
vented by  means  of  a  layer  of  asbestos,  to  obviate  the  formation  of 
copper  silicate. 

7.  Nitrogen  is  usually  estimated  by  DUMAS'S  method.  An 
apparatus  similar  to  that  employed  in  the  estimation  of  carbon 
and  hydrogen  (Fig.  1)  is  used.  The  drying  apparatus  g,  h,  j,  is 
replaced  by  a  carbon-dioxide  KREUSSLER  generator,  to  effect  com- 
plete expulsion  of  the  air  from  the  tube  before  the  combustion  is 
begun.  The  absorption-apparatus  /,  ra,  is  replaced  by  a  delivery- 
tube  opening  under  mercury.  As  soon  as  the  air  has  been  driven 
out  of  the  apparatus,  the  front  part  of  the  tube,  containing  the 
copper-gauze  and  the  granulated  copper  oxide,  is  heated.  The 
combustion  is  then  begun,  and  the  evolved  gases  are  collected  in  a 
graduated  tube  open  at  the  bottom  (measuring  tube),  the  end 
of  which  dips  into  the  mercury-bath.  This  tube  is  filled  partly 
with  mercury,  and  partly  with  concentrated  caustic  potash  to 
absorb  the  carbon  dioxide.  The  reduced  copper-gauze  has  the 
effect  of  decomposing  any  nitrogen  oxides  formed.  When  the 
combustion  is  over,  all  the  nitrogen  remaining  in  the  tube  is  swept 
into  the  graduated  tube  by  a  stream  of  carbon  dioxide  from  the 
KREUSSLER  generator.  The  tube,  along  with  the  mercury,  potash, 
and  gas  which  it  contains,  is  then  placed  in  a  wide  cylinder  filled  with 
water.  The  mercury  and  potash  are  displaced  by  the  water,  and 


8  ORGANIC    CHEMISTRY.  [§  8 

after  the  level  of  the  liquid  inside  and  outside  the  tube  has  been 
made  to  coincide,  the  number  of  cubic  centimetres  of  nitrogen 
is  read  off.  From  this  the  amount  of  nitrogen  in  the  compound 
is  calculated. 

Nitrogen  can  often  be  estimated  by  a  method  discovered  by 
KJELDAHL  and  improved  by  WILFARTH.  It  depends  upon  the 
fact  that  the  nitrogen  of  many  organic  substances  is  wholly  con- 
verted into  ammonia  by  heating  the  compound  for  some  time 
with  concentrated  sulphuric  acid  in  presence  of  phosphoric  oxide 
and  a  drop  of  mercury,  the  latter  going  into  solution.  Usually  the 
mixture  first  turns  black,  owing  to  charring:  after  heating  for 
one  or  two  hours  the  liquid  again  becomes  perfectly  colourless. 
The  carbon  has  then  been  fully  oxidized  by  the  oxygen  of  the 
sulphuric  acid,  which  has  been  reduced  to  sulphurous  acid.  The 
process  is  facilitated  by  the  mercury  salt,  which  probably  plays 
the  part  of  an  "  oxygen-carrier"  between  the  sulphuric  acid  and 
the  organic  substance,  being  continually  converted  from  the  mer- 
curic to  the  mercurous  state,  and  then  back  again  by  the  boiling 
acid  into  the  mercuric  state.  When  the  liquid  has  become  colour- 
less, it  is  allowed  to  cool,  diluted  with  water,  excess  of  alkali  added, 
and  the  ammonia  distilled  into  a  measured  quantity  of  acid  of 
known  strength.  Titration  gives  the  quantity  of  ammonia,  and 
hence  the  amount  of  nitrogen.  This  neat  and  simple  method  is 
usually  not  applicable  to  compounds  containing  oxygen  linked 
to  nitrogen.  In  such  compounds  the  nitrogen  is  only  partially 
converted  into  ammonia. 

8.  The  halogens  can  be  estimated  by  the  method  either  of 
LTEBIG  or  of  CARIUS.  By  the  former,  the  substance  is  heated 
with  quicklime,  and  by  the  latter,  at  a  high  temperature  with  a 
small  quantity  of  concentrated  nitric  acid  and  a  crystal  of  silver 
nitrate  in  a  sealed  glass  tube.  This  is  carried  out  without  risk 
in  the  tube-furnace  (Fig.  3),  in  which  the  glass  tubes  are  placed 
in  wrought-iron  cylinders  with  thick  walls. 

CARIUS 's  method  can  also  be  applied  to  the  estimation  of  sul- 
phur, phosphorus,  and  other  elements.  Non-volatile  substances 
containing  sulphur  or  phosphorus  can  also  be  oxidized  by  fusion 
with  nitre. 

The  estimation  of  halogens  in  solids  can  also  be  readily  effected 
by  oxidation  with  sodium  peroxide,  the  final  product  being  a  chlo- 


§9] 


QUANTITATIVE    ANALYSIS. 


9 


rate,  bromate,  or  iodate.  On  reduction  with  sulphurous  acid,  this 
is  converted  into  a  halide,  which  can  be  precipitated  with  silver 
nitrate  in  the  usual  manner. 

9.  The  results  of  a  quantitative  analysis  are  expressed  in  per- 
centage-numbers. If  the  total  of  these  percentage-numbers  is 
very  nearly  100,  then  no  other  element  is  present  in  the  compound; 
but  if  appreciably  less  than  100,  there  is  another  element  present 
which  has  not  been  taken  account  of  in  the  analysis,  there  being 
no  convenient  method  for  its  estimation.  This  element  is  oxygen. 
The  percentage-amount  of  oxygen  is  therefore  found  by  sub- 
tracting the  total  of  the  percentages  of  the  other  elements  from 


FIG.  3. — TUBE-FURNACE. 

100.     This  has  the  disadvantage  that  all  experimental  errors  are 
included  in  the  percentage-number  of  the  oxygen. 

Carbon-estimations  are  usually  too  low,  owing  to  the  loss  of  a 
small  quantity  of  carbon  dioxide  through  the  various  connections  of 
the  apparatus.  Hydrogen-estimations  are  generally  too  high,  be- 
cause copper  oxide  is  hygroscopic,  and  can  only  be  freed  from  traces 
of  moisture  with  difficulty.  These  errors  balance  one  another  more 


10  ORGANIC    CHEMISTRY.  [§  9 

or  less,  so  that  the  want  of  accuracy  in  the  oxygen-percentage  is 
diminished. 

The  method  by  which  the  percentage  composition  and  formula 
of  a  substance  are  calculated  from  the  results  of  analysis  is  best 
explained  by  an  example. 

The  analysis  of  a  substance  containing  nitrogen  yielded  the  fol- 
lowing numbers: 

0.2169  g.  substance  gave  0-5170  g.  C02  and  0-0685  g.  H2O. 

0-2218  g.  substance  gave  17-4  c.c.  N,  measured  over  water  at 
6°  C.  and  762  mm.  barometric  pressure. 

Since  there  are  12  parts  by  weight  of  C  in  44  parts  by  weight  of 
CO2,  and  2  parts  by  weight  of  H  in  18  parts  by  weight  of  H2O,  the 
number  obtained  for  CO2  must  be  multiplied  by  H =IT  to  find  the 
weight  of  C,  and  the  number  found  for  H2O  by  A  =  ¥  to  obtain  the 
weight  of  H.  This  calculation  gives  65-0  per  cent,  of  carbon  and 
3«51  per  cent,  of  hydrogen  in  the  compound. 

The  weight  of  the  nitrogen  is  calculated  as  follows.  Since  it  is 
saturated  with  water-vapour,  the  tension  of  this  expressed  in  mm. 
of  mercury  must  be  subtracted  from  the  barometric  pressure  in 
order  to  obtain  the  true  pressure  of  the  nitrogen.  At  6°  C.  the 
tension  of  aqueous  vapour  is  7  «0  mm.  The  actual  pressure  of  the 
nitrogen  is  therefore  762  —  7  =  755  mm.  Since  1  c.c.  of  nitrogen  at 
0°  and  760  mm.  weighs  1 .2562  mg.,  at  755  mm.  and  6°  C.  the  weight 
of  this  volume  expressed  in  milligrammes  is 

1 .2562  755 

i+6XO-00367X760  ~ 

Therefore  the  17 '4  c.c.  of  nitrogen  obtained  weigh  1'2211X17'4= 
21  •  247  mg.,  from  which  the  percentage  of  nitrogen  is  found  to  be  9*  6. 
The  sum  of  these  percentage-numbers  is  78»1,  so  that  the  per- 
centage of  oxygen  in  the  substance  analyzed  is  21  -9.    The  percefctage- 
composition  given  by  the  analysis  is  therefore 

C    65-0 
H     3-5 
N     9-6' 
0    21-9 

On  dividing  these  values  by  the  numbers  representing  the  atomic 
weights  of  the  corresponding  elements,  there  results 
C  H  N  0 

5-4        3.5        0.7        1-4. 
These  numbers  divided  by  0-7  give 

C  H  N  0 

7-7        5-0          1-0        2-0. 


10]          DETERMINATION    OF    MOLECULAR    WEIGHT.  11 

These  numbers  approximate  very  close!}'  to  those  required  by 
the  formula  C8H6O2N.  The  percentage-composition  corresponding 
to  this  formula  is 

C  65-3  H  3-4  N  9-5, 

which  agrees  well  with  the  analysis. 


DETERMINATION  OF  MOLECULAR  WEIGHT. 

10.  An  analysis  only  gives  the  empirical  formula  of  a  com- 
pound, and  not  its  molecular  formula,  because  CaHbOc  has  the 
same  percentage-composition  as  (CaHbOc)n.  When  the  empirical 
formula  has  been  ascertained  by  analysis,  the  molecular  weight 
has  still  to  be  determined. 

It  cannot  be  decided  by  chemical  means,  although  it  is 
possible  thus  to  obtain  a  minimum  value  for  the  molecular  weight. 
For  example,  the  empirical  formula  of  benzene  is  CH.  Benzene 
readily  yields  a  compound,  CeH^Br,  which  can  be  reduced  again 
to  benzene.  It  follows  that  the  molecule  of  benzene  must  be 
represented  by  CeH6  at  least.  The  molecular  formula,  however, 
could  also  be  Ci2Hi2,  or,  in  general,  (C6H6)n;  the  bromine  com- 
pound would  then  have  the  formula  (C6H5Br)n.  Assuming  the 
formula  to  be  Ci2Hi2,  that  of  the  bromine  compound  would  be 
Ci2Hi0Br2.  It  is  evident  that  the  formation  of  a  compound  of 
this  formula  would  involve  direct  replacement  of  two  hydrogen 
atoms  by  bromine,  and  experiments  would  be  made  for  the  pur- 
pose of  obtaining  Ci2HnBr.  Should  these  not  attain  the  desired 
result,  the  probability  of  the  correctness  of  the  simpler  formula 
CeH5Br  would  be  increased.  This  would  not,  however,  be  decisive, 
because  the  experimental  conditions  necessary  to  the  formation 
of  the  compound  Ci2HnBr  might  not  have  been  attained.  The 
chemical  method  only  proves  that  the  molecular  formula  of  ben- 
zene cannot  be  smaller  than  C6H6,  but  does  not  prove  whether 
it  is  a  multiple  of  this  or  not. 

To  ascertain  the  real  molecular  weight,  physical  methods  must 
be  employed.  These  involve  the  determination  either  of  the 
specific  gravity  of  the  compound  in  the  gaseous  state,  or  of  cer- 
tain values  depending  on  the  osmotic  pressure  of  the  substance 
in  dilute  solution.  The  theory  of  these  methods  is  fully  ex- 
plained in  "Inorganic  Chemistry."  31-35  and  40-43.  Here  it 


12 


ORGANIC    CHEMISTRY. 


[§H 


will  suffice  to  describe  the  practical  details  of  a  molecular-weight 
determination. 

In  calculating  the  vapour-density  (the  specific  gravity  of  the 
substance  in  the  gaseous  state),  four  quantities — the  weight  of 
substance  converted  into  the  gaseous  state,  the  volume  of  the 
resulting  vapour,  the  temperature  at  which  the  .volume  is  meas- 
ured, and  the  barometric  pressure — must  be  known. 

ii.  Vapour-density  is  usually  determined  by  a  method  sug- 
gested by  VICTOR  MEYER.  The  apparatus  (Fig.  4)  consists  of  a 
glass  tube  B  with  an  internal  diam- 
eter of  about  4  mm.  This  tube  is 
closed  at  the  top  with  a  stopper,  and 
underneath  has  a  wider  cylindrical 
portion  of  about  200  c.c.  capacity, 
closed  at  the  lower  end.  Near  the 
top  of  the  tube  is  sealed  on  a  de- 
livery-tube A  for  the  gas,  which  is 
collected  over  water  in  a  graduated 
tube  E.  The  apparatus  is  partly  sur- 
rounded by  a  wide  glass  (or  metal) 
jacket  C.  This  contains  a  liquid  boil- 
ing higher  than  the  substance  the 
vapour-density  of  which  is  being  de- 
termined. This  liquid  is  heated  to 
boiling,  some  of  the  air  in  B  being 
in  consequence  expelled.  A  point  is 
soon  reached  at  which  no  more  air 
escapes  from  the  delivery-tube,  that 
in  the  wider  part  of  the  tube  having 
a  constant  temperature,  almost  equal 
to  that  of  the  vapour  of  the  boiling 
liquid.  The  graduated  tube  is  then 
filled  with  water  and  placed  over  the 
open  end  of  the  delivery-tube  A. 
After  the  stopper  has  been  withdrawn, 
a  weighed  quantity  of  the  substance 
under  examination  enclosed  in  a  small 
glass  tube  is  dropped  into  the  appa- 
ratus, and  the  stopper  replaced,  care 


FIG.  4. — VICTOR  METER'S 
VAPOUR- DENSITY  APPA- 
RATUS. 


§  11]          DETERMINATION    OF    MOLECULAR    WEIGHT.  13 

being  taken  to  make  it  air-tight.  The  substance  vaporizes  quickly 
in  the  heated  wide  portion  of  the  tube.  Its  vapour  expels  air 
from  the  apparatus:  the  air  is  collected  in  the  graduated  tube, 
and  its  volume  is  equal  to  that  of  the  vapour.  While,  however, 
the  air  in  the  hot  part  of  the  apparatus  has  the  local  temperature, 
in  the  graduated  tube  it  acquires  the  temperature  of  the  latter,  and 
this  must  be  considered  in  making  the  calculation.  The  experi- 
ment gives  a  volume  equal  to  that  which  the  weighed  portion  of 
the  substance  in  the  form  of  vapour  would  occupy,  if  it  were 
possible  to  convert  it  into  a  gas  at  the  ordinary  temperature  and 
under  the  barometric  pressure. 

For  ease  of  manipulation  this  method  leaves  nothing  to  be 
desired.  It  possesses,  moreover,  the  great  advantage  over  the 
other  methods,  that  it  is  not  necessary  to  know  the  temperature 
to  which  the  apparatus  has  been  heated,  this  not  being  employed 
in  the  calculation.  It  is  only  necessary  that  the  temperature 
should  remain  constant  during  the  short  time  occupied  by  the 
experiment. 

The  result  is  calculated  thus.  Suppose  that  g  mg.  of  the  sub- 
stance were  weighed  out,  and  yielded  V  c.c.  of  air,  measured  over 
water,  with  the  level  the  same  inside  and  outside  the  tube:  sup- 
pose further  that  the  barometric  pressure  were  H,  the  tempera- 
ture t,  and  the  tension  of  aqueous  vapour  6,  then,  at  a  pressure 
of  H  —  b  mm.  and  at  t°,  g  mg.  of  the  substance  would  occupy  a 
volume  of  V  c.c.,  so  that  under  these  conditions  the  unit  of  volume 

(1  c.c.)  would  contain  -^  mg.  of  the  substance. 

One  c.c.  of  oxygen  at  H-b  mm.  of  pressure,  and  at  t°, 
weighs  in  milligrammes 

1-429          H-b 


l+0'00367rN  760  ' 

from  which   it  follows   that   the   vapour-density  D  referred  to 
oxygen  =  16  is 

76° 


7  1-429  H=b' 

The  molecular  weight  M  being  twice  the  density, 

M  =  2D. 


14  ORGANIC    CHEMISTRY.  [§  12 

12.  Two  other  methods  are  often  employed  in  the  determina- 
tion of  the  molecular  weights  of  organic  compounds.  They  are 
based  on  the  laws  of  osmotic  pressure,  and  involve  the  determi- 
nation of  the  depression  of  the  freezing-point  or  the  elevation  of 
the  boiling-point  of  a  dilute  solution  of  the  substance,  referred 
to  the  freezing-point  or  boiling-point  respectively  of  the  pure 
solvent  ("Inorganic  Chemistry,"  40-43). 

In  practice,  it  is  necessary  to  determine  first  the  freezing-point 
of  the  solvent;  for  example,  that  of  phenol.  Then  one  gramme- 
molecule  of  a  substance  of  known  molecular  weight  is  dissolved 
in  a  known  weight — that  is,  in  a  known  volume — of  the  solvent,, 

It  lowers  the  freezing-point  by  a  certain  amount,  which  is 
always  the  same  for  the  same  solvent,  no  matter  what  the  substance 
may  be,  provided  that  the  volume  of  solution,  containing  one 
gramme-molecule,  is  the  same.  The  depression  of  the  freezing- 
point  caused  by  a  gramme-molecule  is,  therefore,  a  constant  for 
this  solvent.  If  a  one  per  cent,  solution  of  a  substance  of  unknown 
molecular  weight  M  be  made  in  phenol,  and  the  depression  (A) 
of  the  freezing-point  of  this  determined,  then 

AM  =  Constant ; 

because  the  depression  of  the  freezing-point  is,  between  certain 
limits,  proportional  to  the  concentration. 

It  is  evident  that  this  formula  is  equally  applicable  to  the 
elevation  of  the  boiling-point.  Here  M  is  the  only  unknown 
quantity,  and  can  be  calculated  from  this  equation. 

The  product  AM  is  called  the  molecular  depression  of  the  freezing- 
point  or  the  molecular  elevation  of  the  boiling-point  of  the  solvent. 

Example. — Numerous  determinations  have  proved  that  when 
phenol  is  used  as  the  solvent  the  molecular  depression  of  its 
freezing-point  is  equal  to  75.  We  have  then  for  phenol 

AM  =75. 

A  solution  of  2  »75  per  cent,  concentration  was  prepared  by  dis- 
solving 0-3943  g.  of  a  substance  of  empirical  formula  C7H7ON2  in 
14  -34  g.  of  phenol.  The  depression  of  this  solution  was  0-712°.  For 

0-712 
a  one  per  cent,  solution  the  depression  would  have  been  ~7r  = 


13] 


DETERMINATION    OF    MOLECULAR  WEIGHT. 


15 


0-258,  therefore  A  =  0-258. 
75 


It  follows  that  the  molecular  weight  is 


0-258 


291. 


Since  C7H7ON2  corresponds  with  the  molecular  weight  135,  and 
C14H140.2N4  to  270,  the  latter  comes  nearest  to  the  molecular  weight 
found,  so  that  twice  the  empirical  formula  must  be  assigned  to  the 
compound. 

The  laws  of  osmotic  pressure  only  hold  when  the  solutions  are 
very  dilute.  This  is  also  true  of  the  equation  AM  =  Const.,  since 
it  is  derived  from  these  laws. 

It  is  not  strictly  correct  to  determine  A  by  means  of  a  solu- 
tion of  finite  concentration,  as  is  done  in  the  example  given. 

To  determine  M  accurately,  the  value  of  A  should  be  derived 
from  a  solution  of  infinite  dilution;  but  as  this  is  not  possible, 

EYKMAN  has  described  the  following 
graphic  method  of  determining  A  for 
such  a  solution.  A  is  determined  for 
three  or  four  concentrations,  and  the 
values  obtained  are  represented  graphic- 
ally as  in  Fig.  5,  in  which  the  values 
of  A  are  the  ordinates,  and  those  of 
the  percentage-strengths  of  the  solu- 
tions are  the  abscissae.  EYKMAN  states 
that  very  often  the  line  drawn  through 
the  tops  of  the  ordinates  is  very  nearly 
straight.  If  it  is  produced  till  it  cuts  the  ordinate  OA,  OP0  gives 
the  value  of  A  for  infinite  dilution. 

13.  The  constants  for  the  molecular  depression  of  the  freezing- 
point  of  a  number  of  solvents  are  given  in  the  following  table: 


PERCENTAGES 

FIG.  5. — EYKMAN'S  GRAPHIC 
METHOD. 


Solvent. 

Melting-point. 

Molecular  Depression. 

Observed. 

Calculated. 

Water 

0° 
16-5° 
6° 
5° 
39-6° 
80° 
48-7° 
53° 
42-5° 

19 
39 
53 
70 
75 
69 
51-4 
45 
52.4 

18-9 
38-8 
53 
69-5 
77 
69-4 

Acetic  acid 

Benzene 

Nitrobenzene     .  .               ... 

Phenol                             

Naphthalene  

Urethane  

Stearic  acid 

7>-Toluidine 

16 


ORGANIC    CHEMISTRY. 


[§14 


The  last  five  solvents  are  very  useful,  and  are  better  than 
glacial  acetic  acid,  which  is  still  often  employed,  because  they  are 
not  hygroscopic.  Moreover,  they  melt  above  the  ordinary  tem- 
perature, so  that  a  cooling  agent  is  unnecessary,  and  their  con- 
stants are  high. 

The  following  table  shows  that  the  molecular  elevations  of  the 
boiling-point  are  usually  smaller  than  the  molecular  depressions  of 
the  freezing-point. 


Molecular 

Elevation. 

Solvent. 

Boiling-point. 

Observed. 

Calculated. 

Water  

100° 

5^1 

5-2 

Ether 

35-6° 

22.1 

2i.i 

Ethyl  alcohol 

78-0° 

11-3 

11-5 

Benzene 

80-4° 

26-0 

26-7 

Chloroform.  . 

61-0° 

35-  G 

36*6 

Acetone 

56-3° 

17-3 

16.7 

The   numbers    in    the  last    column    of   the   tables    are   cal- 
culated from  VAN'T  HOFF'S  formula 


K 


K  being  the  molecular  depression  or  elevation,  T  the  freez- 
ing-point or  boiling-point  on  the  absolute  scale,  and  W  the 
latent  heat  of  fusion  or  of  evaporation  per  kilogramme  of  the 
solvent. 

14.  EYKMAN  has  constructed  convenient  apparatuses  for  the 
determination  of  the  depression  of  the  freezing-point  and  the 
elevation  of  the  boiling-point.  The  first  (Fig.  6)  comprises  a  small 
thermometer  divided  into  twentieths  of  a  degree  with  a  small 
flask  attached  as  shown  in  the  figure,  this  being  contained  in  a 
glass  cylinder:  it  is  held  at  the  top  by  a  stopper,  and  supported 
underneath  by  cotton-wool.  The  latter  has  the  effect  of  making 


15] 


DETERMINATION  OF  MOLECULAR   WEIGHT. 


17 


the  cooling  take  place  slowly.  Being  a  poor  conductor  of  heat, 
the  cotton-wool  retards  cooling.  A  weighed  quantity  of  the  solvent 
is  placed  in  the  flask,  and  its  freezing-point  determined.  Then 
a  known  weight  of  the  substance  is  introduced,  and  the  freezing- 
point  again  observed.  From  the  depression  of  the  freezing-point 
thus  obtained  A  can  be  calculated  as  in  the  example  given  (12). 


^ . 


T 


K) 

X) 


FIG.  6. — EYKMAN'S 
DEPRESSIMETER. 


FIG.  7. — EYKMAN'S  BOILING- 
POINT  APPARATUS. 


15.  EYKMAN'S  apparatus  (Fig.  7)  for  determining  the  eleva- 
tion of  the  boiling-point  comprises  a  thermometer,  and  two  glass 
vessels,  A  and  B.  The  tube  A  is  about  40  cm.  long  and  4  cm. 
wide,  and  serves  both  as  a  heating  jacket  for  the  pure  solvent, 
and  as  an  air-condenser.  Into  B,  which  is  only  a  few  millimetres 


18  ORGANIC   CHEMISTRY.  [§  15 

narrower  than  A,  there  is  fused  the  boiling-tube  C,  with  a  narrow 
side-tube  D.  C  is  suspended  from  the  clamp  K  by  a  platinum  wire, 
P,  twisted  round  its  neck,  and  can  be  raised  or  lowered  at  will. 
The  thermometer-scale  is  divided  into  tenths  of  a  degree,  the 
graduations  being  about  one  millimetre  apart,  so  that  with  the 
aid  of  a  lens  it  is  possible  to  read  to  one-hundredth  of  a  degree. 
Besides  giving  the  boiling-point,  the  graduated  scale  of  the  ther- 
mometer also  serves  to  indicate  the  volume  of  solution  contained 
in  C.  For  this  purpose  the  vessel  C  with  the  thermometer  placed 
in  it  must  be  calibrated  by  a  gravimetric  or  volumetric  method. 

When  using  the  apparatus  the  solvent  is  introduced  into  C 
until  the  level  of  the  liquid  has  risen  to  that  of  the  first  gradu- 
ation on  the  thermometer-scale,  from  5  to  10  c.c.  being  needed. 
About  40  or  50  c.c.  of  the  solvent  are  poured  into  the  jacket  A, 
and  the  apparatus  heated  with  a  micro-burner,  using  a  large  flame 
ut  first.  When  ebullition  has  begun,  the  size  of  the  flame  is  re- 
duced so  that  the  vapour  is  completely  condensed  in  the  tube  A 
at  a  height  shown  in  the  figure  by  the  letters  A  or  E. 

When  the  liquid  has  boiled  at  a  constant  temperature  for  a  short 
time,  the  height  of  the  mercury  is  noted,  and  the  clamp  raised  so 
that  the  open  end  of  the  boiling-tube  C  is  some  centimetres  above 
the  top  of  the  jacket  A.  A  weighed  quant  it  y+ 1-2  milligramme- 
molecules — of  the  substance  under  investigation  is  then  introduced 
into  C  from  a  tared  weighing-tube,  and  C  gently  lowered  to  its 
former  position  in  the  jacket.  While  the  weighing-tube  is  being 
weighed  to  ascertain  how  much  substance  has  been  added,  the 
boiling-point  of  the  solvent  will  have  become  constant.  This  is 
noted,  the  boiling-tube  C  again  raised  by  the  aid  of  the  clamp  K, 
and  the  volume  accurately  determined  by  reading  with  a  lens  the 
height  of  the  solution-meniscus  on  the  thermometer-scale. 

A  second  determination  is  made  with  a  solution  of  greater 
concentration  by  introducing  a  further  quantity  of  the  substance 
from  the  weighing-tube,  and  repeating  the  series  of  operations 
just  described.  Since  very  little  more  time  is  needed  for  each 
operation  than  is  required  to  tare  the  weighing-tube  and  its  con- 
tents, a  series  of  determinations  at  different  concentrations  can 
be  quickly  made,  and  the  results  plotted  on  squared  paper.  From 
the  curve  thus  obtained  the  value  of  A  for  infinite  dilution  can 
be  readily  calculated  (12). 


|§  16,  17]  THE   ELEMENT   CARBON.  1Q 

THE   ELEMENT   CARBON. 

16.  Carbon  occurs  in  three  allotropic  forms:  diamond,  graphite, 
and  amorphous  carbon.     For  a  description  of  these  the  reader  is 
referred  to  "  Inorganic  Chemistry/'  176-179,  which  also  treats  of 
the  compounds  of  carbon  with  metalloids  and  metals,  as  well  as 
with  the  determination  of  its  atomic  and  molecular  weights.     The 
evidence  in  favour  of  the  assumption  that  the  molecule  of  carbon 
contains  a  great  number  of  atoms  is  there  set  forth. 

Confirmation  of  this  view  is  afforded  by  a  consideration  of  the 
relation  subsisting  between  the  boiling-points  of  the  compounds 
of  carbon  and  of  hydrogen.  Jf  these  be  denoted  by  the  general 
formula  CnH2n_p,  then,  even  when  n  and  p  are  both  large  num- 
bers, the  boiling-points  of  these  substances  are  relatively  low,  and 
rise  with  the  increase  of  both  n  and  p.  For  carbon  itself,  2n  =  p, 
and,  on  account  of  the  extraordinary  non-volatility  of  this  sub- 
stance, the  value  of  n  must  be  very  great. 

The  subject  of  valency  is  treated  of  in  "  Inorganic  Chem- 
istry/' 76.  With  univalent  elements  carbon  forms  compounds 
of  the  type  CX4.  It  is  therefore  quadrivalent,  and  it  is  on  this 
foundation  that  the  whole  superstructure  of  organic  chemistry 
rests. 

The  compound  C02  is  also  an  instance  of  the  quadrivalency  of 
carbon.  In  carbon  monoxide,  CO,  on  the  other  hand,  the  carbon 
atom  must  be  looked  upon  as  bivalent,  at  least  if  the  bivalency  of 
oxygen  is  retained.  Other  compounds  are  well  known  in  which 
carbon  may  be  looked  upon  as  bivalent,  but  their  number  is  very 
small  in  comparison  with  those,  numbering  many  thousands,  in 
which  carbon  must  be  regarded  as  quadrivalent. 

LABORATORY-METHODS. 

17.  To  prevent  repetition,  it  is  desirable,  before  proceeding 
with  a  description  of  the  organic  compounds,  to  give  a  short  account 
of  the  most  important  operations  used  in  their  preparation  and 
investigation. 

Heating  Substances  Together. — This  process  is  very  often  used 
to  induce  reaction  between  bodies,  since  the  velocity  of  reac- 
tions increases  largely  with  rise  of  temperature  ("  Inorganic 
Chemistry,"  13  and  104).  Details  vary  according  to  the  tem- 


20 


ORGANIC  CHEMISTRY. 


[§17 


perature  to  be  attained.  If  this  is  considerably  below  the  boil- 
ing-point of  the  most  volatile  compound,  they  are  simply 
mixed  together  in  a  flask  fitted  with  a  thermometer,  as  in  Fig,  8, 
The  flask  is  immersed  in  an 
air-bath  formed  of  a  vertical 
iron  cylinder  closed  at  the 
lower  end,  a  piece  of  stove- 
pipe being  very  suitable.  The 
upper  end  is  closed  with  a 
sheet  of  asbestos  mill-board, 
with  an  opening  for  the  neck 
of  the  flask.  Should,  how- 
ever, the  boiling-point  of  one 
of  the  substances  be  reached 
or  overstepped,  the  flask 
must  be  connected  with  a 
condenser,  as  in  Fig.  9.  The 
invention  of  this  form  of  con- 
densing apparatus  is  usually 


FIG.  8.  —  HEATING 
SUBSTANCES  IN  AN 
OPEN  FLASK. 


FIG.  9.  —  FLASK 
WITH  REFLUX- 
CONDENSER. 


attributed  to  LIEBIG,  although  it  was  first  constructed  by  WETGEL 
in  1771.  It  consists  of  a  glass  tube  aa,  enclosed  in  a  jacket  6  of 
glass  or  metal,  through  which  a  stream  of  cold  water  can  pass.  For 
substances  of  high  boiling-point  a  plain  vertical  glass  tube  may 


$  18] 


LABORA  TORY-  METHODS. 


21 


be  substituted:  it  is  called  an  "air-condenser,"  being  sufficiently 
cooled  by  the  air  alone.  The  effect  of  the  condenser  is  evident: 
the  boiling  liquid  is  condensed  in  it  and  drops  back  into  the  flask. 


FIG.  10. — DISTILLATION-APPARATUS. 

When  substances  have  to  be  heated  above  their  boiling-points, 
they  are  placed  in  a  thick-walled  glass  tube  sealed  at  one  end: 
this  is  then  sealed  at  the  other,  and  heated  in  a  tube-furnace 
<9,  Fig.  3). 

18.  Distillation. — The  apparatus  shown  in  Fig.  10  may  be  used, 

but  if  the  liquid  to  be  distilled 
is  of  such  a  nature  that  it  would 
become  contaminated  by  the 
action  of  its  vapour  on  the  cork 
or  rubber  stopper  shown  in  the 
figure,  a  distilling-flask  (Fig.  11) 
is  substituted,  and,  if  its  neck 
is  sufficiently  long,  contact  of  the 
vapour  with  the  stopper  during 
distillation  is  prevented. 

At     the     ordinary    pressure 
many   substances   decompose  on 
heating    to    their    boiling-points, 
but   distil   unchanged   under   di- 
minished   pressure,    because    the 
FIG.  11.— FRACTIONATING-FLASK.      boiling-point  is  then  much  lower. 
The   apparatus   shown   in   Fig.  12  can   be  used  for  vacuum-dis- 
tillation. 


22 


ORGANIC    CHEMISTRY. 


II 


The  liquid  to  be  distilled  is  placed  in  d.  A  glass  tube  e,  drawn 
out  to  a  very  fine  point,  dips  into  the  liquid,  and  a  thermometer 
is  placed  in  it.  As  soon  as  the  apparatus  has  been  made  vacuoiis 
by  the  water-pump  w,  a  stream  of  small  bubbles  of  air  escapes 
from  the  fine  point  of  the  tube  e,  and  serves  to  prevent  the  violent 
"bumping"  which  otherwise  occurs  when  liquids  are  boiled  under 
diminished  pressure.  This  bumping,  caused  by  the  sudden  and 
intermittent  formation  of  vapour,  sometimes  causes  boiling  over, 
or  fracture  of  the  flask.  The  receiver  b  is  kept  cool  by  a  stream 
of  water  from  c.  m  is  a  mercury  manometer:  a  is  a  two-way 


FIG.  12. — DISTILLATION  IN  VACUUM. 

stop-cock  which  permits  access  of  air  to  the  apparatus  after  the 
distillation,  and  also  serves  to  cut  off  the  connection  between  the 
air-pump  and  the  rest  of  the  apparatus  when  the  pump  "strikes 
back  ";  that  is,  when  the  water  rises  through  the  tube  s  into  the 
apparatus. 

19.  The  separation  of  a  mixture  of  volatile  substances  is  effected 
by  fractional  distillation.  If  a  mixture  of  two  liquids,  boiling,  for 
example,  at  100°  and  at  130°,  is  distilled,  more  of  that  boiling  at 
100°  distils  over  at  the  beginning,  and  more  of  that  boiling  at  130° 
at  the  end,  of  the  operation.  If  the  distillate  passing  over  below 
110°  is  collected  separately  in  one  fraction,  and  similarly  that 
between  120°  and  130°,  a  rough  separation  is  effected,  while  the 
middle  fraction  still  consists  of  a  mixture.  To  make  the  separa- 


§20]  FRACTIONAL   DISTILLATION.  23 

tion  as  complete  as  possible,  the  fraction  100°-110°  is  returned 
to  the  fractionation-flask  and  distilled  till  the  thermometer  reaches 
110°,  the  fraction  110°-120°  then  mixed  with  the  residue  in  the 
fractionation-flask,  and  the  distillation  then  continued  till  the 
thermometer  again  stands  at  110°.  The  receiver  is  changed,  and 
the  distillation  renewed  till  the  thermometer  reaches  120°.  The 
fraction  120°- 130°  is  then  added  to  the  liquid  in  the  distillation- 


Young.  HEMPEL.  WURTZ.  LINNEMAN. 

FIG.  13. — FRACTIONATING-COLUMNS. 

flask,  and  the  distillate  collected  in  the  same  receiver,  until  the  ther- 
mometer again  indicates  - 120°.  The  portion  distilling  subse- 
quently is  collected  separately.  By  several  repetitions  of  this  process 
it  is  possible  often  to  effect  an  almost  complete  separation,  it  being 
usually  advantageous  to  collect  the  fractions  between  narrower 
limits  of  temperature,  and  thus  to  increase  their  number. 

20.  The  separation  is  much  facilitated  by  using  a  fractionating- 
column    (Fig.    13)    connected   to  the   neck   of  the    boiling-flask; 


24  ORGANIC    CHEMISTRY.  [§21 

the  vapour  of  the  least  volatile  constituents  of  the  mixture  is  to 
a  large  extent  condensed  in  the  column.  The  stream  of  vapour 
from  the  distillation-flask  heats  the  liquid  in  the  fractionating- 
column,  the  effect  being  to  vaporize  its  more  volatile  part,  and 
simultaneously  to  condense  the  higher-boiling  constituent  of  the 
vapour  issuing  from  the  flask. 


21.  A  change  in  the  composition  of  most  liquid  mixtures  does 
not  occasion  a  proportional  alteration  in  their  properties,  like  that 
expressed  in  the  annexed  graphic  representation  (Fig.  14)  by  a  straight 
line  AB.  The  abscissae  correspond  with  the  molecular-percentage 
composition  of  the  mixtures:  the  points  A  and  B  on  the  ordinates 
give  the  values  of  such  physical  constants  as  vapour-tension,  boiling- 
point,  specific  gravity,  etc..  for  the  pure  substances  A  and  B,  and 
the  line  AB  the  values  of  these  constants  for  mixtures.  The 
curve  thus  obtained  usually  varies  more  or  less  from  a  straight 
line. 

The  boiling-points  of  mixtures  will  be  lower  (line  c)  or  higher 
(line  6)  than  those  calculated  by  the  proportion-rule.  Sometimes, 
these  boiling-point  curves  will  depart  so  much  from  the  straight 
line  as  to  show  such  maxima  and  minima  as  the  curves  a  and  d. 
Complete  separation  of  such  mixtures  by  fractional  distillation  at 
constant  pressure  is  impossible,  but  is  feasible  when  the  boiling- 
point  curves  follow  the  course  indicated  by  b  or  c.  The  most 
volatile,  or  lowest  boiling,  constituent  of  a  mixture  always  distils 
first,  so  that  the  vapour  is  richer  in  A  and  the  residual  liquid  in  B. 
If  the  pure  constituents  A  and  B  are  more,  or  less,  volatile  than 
any  mixture  of  the  two,  as  represented  by  the  boiling-point  curves 
b  and  c,  continued  fractional  distillation  must  lead  to  an  approxi- 
mately complete  separation  of  A  and  B.  But  if  the  boiling-point 
curve  has  a  maximum  or  minimum,  the  mixtures  corresponding 
with  it  will  consist  of  the  most,  or  least,  volatile  constituents.  On 
distillation,  a  fraction  with  this  highest,  or  lowest,  boiling-point  will 
always  be  obtained,  and  at  constant  pressure  further  separation 
will  be  impossible. 

Comprehension  of  this  phenomenon  will  be  facilitated  by  con- 
sidering a  boiling-point  curve  b  without  a  maximum  or  minimum 
(Fig.  15).  Since  the  most  volatile  portion  of  any  mixture  always 
volatilizes  first,  the  vapour  evolved  from  a  boiling  liquid  always 
contains  more  of  A  than  the  liquid  itself.  When  the  composition 
of  the  mixture  is  6,  that  of  the  liquid  will  be  b'.  The  vapour-tension 


§21] 


FRACTIONAL    DISTILLATION. 


25 


curve  Ab'B  throughout   the   complete   trajectory  AB  lies    higher 
than  the  boiling-point  curve. 

If  the  boiling-point  curve  has  a  maximum  b  (Fig.  16),  along  the 
trajectory  Ab  the  vapour  will  be  richer  in  A  than  the  liquid  from 


Percentages  100 

FIG.  14. 


Percentages 
FlG.  15. 


100 


0  Percentages  100 

FIG.  16. 
FRACTIONAL-DISTILLATION  CURVES. 

which  it  is  evolved:  along  the  trajectory  bB  the  vapour  will  contain 
more  of  B  than  the  liquid,  since  B  is  now  the  most  volatile,  or 
lowest  boiling,  constituent.  It  follows  that  at  the  maximum  b 
the  vapour  must  have  exactly  the  same  composition  as  the  liquid,- 
that  is,  the  mixture  with  maximum  boiling-point  distils  at  a  constant 
temperature  as  though  it  were  a  single  substance.  For  a  mixture 
of  liquids  with  a  minimum  boiling-point  analogous  results  aw 


26  ORGANIC    CHEMISTRY.  [§22 

obtained,  so  that  in  the  graphic  representation  the  vapour-tension 
curve  must  be  tangential  to  the  boiling-point  curve,  and  touch  it 
at  the  minimum-point. 

The  separation  of  a  mixture  of  liquids  by  fractionation  is  also 
impossible  when  the  boiling-points  of  its  constituents  are  close 
together,  because  the  essential  characteristic  of  the  whole  method 
consists  in  the  unequal  volatility  of  the  portions  composing  the 
mixture,  resulting  in  the  distillation  of  one  substance  before  the 
other.  If,  however,  the  substances  have  nearly  the  same  boiling- 
point,  then  both  attain  a  vapour-tension  of  one  atmosphere  at  al- 
most the  same  temperature ;  in  other  words,  they  are  almost  equally 
volatile.  With  these  conditions  it  is  therefore  impossible  to  apply 
the  method  successfully. 

22.  Steam-distillation.  —  In  the  preparation  of  many  organic 
substances  a  crude  reaction-product  is  often  obtained  containing 
tarry  matter  along  with  the  required  compound.  To  free  the 
substance  from  this,  use  is  often  very  advantageously  made  of  the 
property  possessed  by  many  substances  of  distilling  in  a  current 
of  steam,  the  tarry  matter  remaining  behind.  Fig.  17  shows  the 
apparatus  employed  in  such  a  distillation. 

Water  is  boiled  in  the  can  a,  fitted  with  a  delivery-tube  c  and 
a  safety-tube  6,  the  evolved  steam  being  passed  into  the  bottom 
of  the  distillation-flask  d.  If  the  distillation  is  interrupted,  cooling 
causes  diminished  pressure  in  a,  air  being  then  able  to  enter  the 
tube  b.  If  6  were  not  used,  the  liquid  in  d  would  flow  back  into 
a,  owing  to  the  fall  in  the  steam-pressure. 

Steam-distillation  is  also  of  service  in  separating  compounds- 
volatile  with  steam  from  others  not  volatile.  With  substances  in- 
soluble in  water,  the  distillate  is  a  milky  liquid,  because  the  water 
in  the  receiver  is  mixed  with  fine,  oily  drops.  There  is  also  an  oily 
layer  above  or  below  the  water. 

In  steam-distillations  two  liquids  take  part — water  and  the  sub- 
stance to  be  distilled.  Usually  these  liquids  are  not  miscible  in  all 
proportions.  In  the  limiting  case,  when  each  liquid  is  wholly  insoluble 
in  the  other,  the  vapour-pressure  of  each  is  unaffected  by  the  presence 
of  the  other.  At  the  boiling-point  of  the  mixture,  the  sum  of  the 
vapour-pressures  of  the  two  constituents  must  be  equal  to  the  baro- 
metric pressure,  since  the  liquid  is  boiling.  The  boiling-point  must 
be  lower  than  that  at  ordinary  pressure  of  the  lower-boiling  of  the  two 
substances,  because  the  partial  pressure  is  necessarily  smaller  than 


STEAM-DISTILLATION. 


27 


the  total  pressure,  which  is  equal  to  that  of  the  atmosphere.  The 
same  result  is  therefore  attained  as  by  distillation  at  diminished 
pressure;  that  is,  the  volatilization  of  the  substance  at  a  tem- 
perature lower  than  its  boiling-point  under  ordinary  pressure. 

Whether  a  substance  distils  quickly  or  slowly  with  steam  de- 
pends on  its  partial  pressure  and  on  its  vapour-density,  together  with 


FIG.  17. — STEAM-DISTILLATION. 

the  values  of  these  physical  constants  for  water.  If  the  pressures 
are  p\  and  ^2,  and  the  vapour-densities  di  and  dz,  the  quantities  dis- 
tilling simultaneously  are  pidi  (substance)  and  p2ds  (water).  If  the 
ratio  7?!^,  :p2d2  is  large,  the  substance  distils  with  a  small  quantity  of 
water,  the  distillation  being  quickly  completed.  The  reverse  takes 
place  when  the  ratio  p}dt  :p2d?  is  small. 

At  a  pressure  of  760  mm.  a  mixture  of  nitrobenzene  and  water 
boils  at  99°.  The  steam  exerts  a  pressure  of  733  mm.,  so  that 
the  tension  of  the  nitrobenzene-vapour  is  27  mm.  Since  the  vapour- 
densities  of  water  and  nitrobenzene  are  in  the  ratio  of  their 
respective  molecular  weights,  18  and  123,  the  proportion  of  water 
to  nitrobenzene  in  the  distillate  should  be  as  733x18  :  27x1 23; 
that  is,  approximately  as  4  :  1.  Notwithstanding  its  small  vapour- 
tension  at  the  boiling-point  of  the  mixture,  the  quantity  of  nitro- 
benzene which  passes  over  is  about  one-fifth  of  the  total  distillate, 
the  rapid  volatilization  of  the  nitrobenzene  being  due  to  the  fact 
that  it  has  a  large,  and  water  a  small,  molecular  weight.  Even. 


28  ORGANIC  CHEMISTRY.  [§23 

when  an  organic  compound  under  similar  conditions  has  a  vapour- 
tension  of  only  10  mm.,  it  distils  with  steam  sufficiently  rapidly 
to  render  the  method  applicable  to  its  purification. 

23.  Separation  of  Two  Immiscible  Liquids. — For  this  purpose, 
a  separating-funnel  (Fig.  18)  is  employed:  the  method  can  be 
inferred  from  the  drawing  without  further  explanation. 
It  is  also  applied  to  the  extraction  of  aqueous  solu- 
tions of  substances  soluble  in  a  volatile  liquid  im- 
miscible with  water,  such  as  ether,  light  petroleumr 
chlorofonn,  carbon  disulphide.  The  solution  is  trans- 
ferred to  a  separating-funnel;  ether,  if  that  solvent 
is  selected,  is  added;  and  after  the  mouth  of  the 
funnel  has  been  closed  by  a  glass  stopper,  the  two 
liquids  are  mixed  together  by  vigorous  shaking, 
whereupon  the  substance  dissolved  in  the  water 
passes  partly  into  the  ether.  The  ethereal  solution 
is  allowed  to  rise  to  the  surface,  and  separated  from 
the  water  by  opening  the  stop-cock  after  removal 
1  RATING- FUN-  °*  tne  stopper.  The  water  dissolved  by  the  ether 
NEL.  during  the  shaking  is  removed  by  chloride  of  cal- 

cium, or  some  other  drying  agent,  and  finally  the  ether  is  distilled 
off.  When  the  dissolved  substance  is  only  slightly  soluble  in 
water,  and  easily  soluble  in  ether,  the  extraction  is  completed 
quickly;  it  is  then  possible  to  exhaust  the  aqueous  solution  almost 
completely  by  several  repetitions  of  the  process,  using  fresh  ether 
for  each  extraction.  Otherwise,  the  shaking  must  be  repeatedly 
carried  out,  and  even  then  the  extraction  is  imperfect. 

When  two  immiscible  solvents  are  simultaneously  in  contact  with 
a  substance  soluble  in  both,  the  latter  distributes  itself  so  that  the 
ratio  of  the  concentrations  reached  in  both  solvents  is  constant 
(law  of  BERTHELOT).  If  a  quantity  X0  of  the  substance  is  dis- 
solved in  a  quantity  I  of  the  first  solvent  (water),  and  this  solution 
extracted  with  a  quantity  m  of  the  second  solvent  (ether),  there  will 
then  remain  a  quantity  Xi  in  the  first  solution,  so  that  X0  —  X>  has 
passed  into  the  second  solvent. 

The  value  of  the  quantity  Xi  is,  in  accordance  with  the  above 
law,  given  by  the  equation 


— — , 

+  Ki 


§  23]  EXTRACTION  WITH  SOLVENTS.  29-> 

X          X  —X\ 

for  —  -  and  —  -  -  are  the  two  concentrations  after  agitation  with 
/  m 

the  solvents,  and  K  is  the  number  expressing  the  constant  ratio,  or 
the  coefficient  of  distribution  (German,  Teilungskoeffizient}. 

A  second  extraction  with  the  same  quantity  m  of  the  second 
solvent  gives 

X-2         j-rX*  ~X-2 

T~-r^r~' 

or,  substituting  the  value  of  X^  from  the  first  equation, 


and  for  the  nth  extraction, 


Thus  Xn,  the  quantity  remaining  in  the  first  solvent  (water),, 
diminishes  as  n  increases,  and  as  m  and  K  are  respectively  greater 
and  less.  Complete  extraction  is  impossible,  because  although- 

(  -  —  )    can  approach  zero  very  closely,  it  can  never  become 
\m+Kl/ 

equal  to  it. 

Examples  will  facilitate  comprehension  of  this  formula.  Sup« 
pose  the  problem  is  to  determine  how  often  1000  c.c.  of  an  aqueous 
solution  of  benzoi'c  acid  must  be  extracted  with  200  c.c.  of  ether  to 
remove  all  the  benzoi'c  acid  from  the  solution.  In  this  instance 
Z  =  1000  c.c.,  and  m=200  c.c.  By  experiment  K  is  found  to  have 
approximately  the  value  *u;  that  is,  if  the  concentration  of  the 
benzole  acid  in  the  ethereal  solution  is  represented  by  80,  that  in 
the  aqueous  solution  is  expressed  by  1.  On  substituting  these 
values  for  I,  m,  and  K  respectively,  the  formula  becomes 

X         Kl  IQOQX^ 


which  means  that  a  single  extraction  with  200  c.c.  of  ether  leaves  iV 
of  the  benzole  acid  in  the  aqueous  solution.     After  three  extrac- 

tions with  200  c.c.  of  ether,  there  remains  only  I  —  j    =T^  of  the 


acid,  so  that  the  extraction  of  the  acid  is  practically  complete. 
For  succinic  acid  K  =  Q.    A  single  extraction  of  1000  c.c.  of  an- 


30 


ORGANIC    CHEMISTRY. 


[§§  24,  25 


aqueous    solution    of    this    acid    with    200    c.c.    of   ether    leaves 

Repeated 


6000          30 

— - — 77^  =  ^7  of  the  acid  still  dissolved  in  the  water 
200  ~\~  oOOO     o  1 


extraction  is  necessary  to  remove  all  the  succinic  acid   from    the 

aqueous  solution. 

It  can  be  further  shown  from  the  equa- 
tion by  the  use  of  the  differential  calculus 
that  with  a  given  quantity  of  the  second 
solvent  (ether)  a  more  complete  separa- 
tion is  effected  by  extracting  frequently 
with  small  quantities  than  by  using 
larger  quantities  a  correspondingly  fewer 
number  of  times. 


FIG    19. — FILTERING- 
FLASK. 


Separation  of  Solids  and  Liquids.— 
This  is  effected  by  filtration,  a  process 
materially  accelerated  by  attaching  the 
funnel  with  a  rubber  stopper  to  a  flask 
a  (Fig.  19),  connected  through  6  to  a 
water  air-pump.  To  prevent  rupture  of 
the  point  of  the  filter-paper,  it  must  be 
supported  by  a  hollow  platinum  cone  c. 

24.  Separation  of  Solids  from  one  Another. — This  process  de- 
pends on  difference  in  solubility.    For  a  soluble  and  an  insoluble 
substance    the   operation  is  very  simple.     If  both  substances  are 
soluble,  the   method   of   fractional  crystallization   must   be   used. 
The  mixture  is  dissolved  in  the  minimum  quantity  of  a  boiling 
liquid:  on  cooling  the  solution  the  less  soluble  substance  crystallizes 
first.     The  mother-liquor  is  poured  off  just  as  crystals  of  the  second 
body  begin  to  separate,  and  the  second  compound  crystallized  either 
by  further  cooling  or  by  concentrating  the  liquid  by  evaporation. 
Several  repetitions  of  these  processes  are  essential  to  the  separa- 
tion.     Even  when  the  pure  compounds  have  very  different  solu- 
bilities, the  method  is  not  free  from  difficulty,  because  the  solu- 
bility of  one  substance  may  be  very  considerably  modified  by  the 
presence  of  another.     Water,  alcohol,  ether,  glacial  acetic  acid, 
benzene,  and  other  substances  are  employed  as  solvents. 

25.  From  the   foregoing  it  is  seen  that  solid  substances  are 
usually  purified  by  crystallization,  and  liquids  by  distillation.     It 
is  an  indication  of  purity  when  the  physical  constants  remain  un- 
changed after  the  substance  has  been  purified  anew.    Although 


25] 


MELTING-POINTS  AND  BOILING-POINTS. 


31 


every  physical  constant  could  serve  this  purpose,  the  melting- 
point  and  the  boiling-point  are  those  most  used,  because  they  are 
easily  determined,  and  slight  impurities  exercise  a  very  material 
influence  upon  them.  They  also  often  afford  a  means  of  identify- 
ing substances.  If  a  compound  has  been  ob- 
tained by  some  process  and  is  supposed  to  be 
one  already  known,  it  is  strong  evidence  in 
favour  of  the  supposition  if  the  melting-point 
and  boiling-point  of  the  substance  coincide 
with  those  of  the  compound  with  which  it  is 
supposed  to  be  identical.  For  this  reason 
determinations  of  melting-points  and  boiling- 
points  are  very  often  carried  out. 

The  best  method  of  ascertaining  whether 
two  substances  are  identical  is  to  mix  them  in 
approximately  equal  proportions  and  determine 
the  melting-point  of  the  mixture.  When  iden- 
tity exists,  the  melting-point  of  the  mixture  will 
coincide  with  that  of  the  two  individual  sub- 
stances;  when  it,  does  not,  the  mixture  melts 
at  a  much  lower  temperature,  which  is  not 
sharply  denned. 

THIELE  has  devised  a  very  convenient  apparatus  for  deter- 
mining the  melting-point  (Fig.  20).  A  small  quantity  of  the 
substance  is  placed  in  a  thin-walled  capillary  tube  sealed  at  one 
end.  This  tube  is  attached  to  a  thermometer,  T,  with  its  bulb 
dipping  into  a  liquid  of  high  boiling-point,  such  as  concentrated 
sulphuric  acid,  olive  oil,  or  liquid  paraffin  (31),  the  viscosity 
causing  the  tube  to  adhere  to  the  thermometer.  The  liquid  is 
contained  in  the  apparatus  ABC.  Heating  with  a  small  flame 
at  B  induces  circulation  of  the  liquid,  ensuring  uniform  heat- 
ing of  the  thermometer  and  capillary  tube.  When  the  sub- 
stance fuses,  the  thermometer  is  read. 

The  boiling-point  is  determined  by  heating  the  liquid  to  boil- 
ing in  a  fractionation-flask  with  a  high  side-tube.  Short  ther- 
mometers are  used,  so  that  the  whole  of  the  mercury  column  is 
surrounded  by  the  vapour  of  the  boiling  liquid.  To  avoid  in- 
conveniently small  graduations,  these  thermometers  are  con- 
structed so  that  they  can  only  be  employed  for  a  comparatively 


G  20.—  THIELE'S 
MELTING-POINT 
APPARATUS. 


32  ORGANIC  CHEMISTRY.  [§26 

small  range  of  temperature,  six  or  seven  different  instruments 
being  used  for  temperatures  between  0°  and  360°.  These  are 
called  "  abbreviated  "  thermometers. 

26.  Sometimes  physical  constants  other  than  the  melting-points 
and  boiling-points  are  determined  in  the  investigation  of  organic 
7  compounds.     1.  The  specific  gravity  can  be  de- 

termined with  the  pyknometer,  the  most  useful 
form  of  which  is  shown  in  Fig.  21.  It  consists 
of  two  thick-walled  capillaries  a  and  b,  termi- 
nating in  a  wider  tube  c.  The  parts  a  and  b  are 
furnished  with  a  millimetre-scale.  The  capacity 
of  the  apparatus  is  first  determined,  as  well  as 
that  of  the  space  between  two  divisions,  by 
filling  it  several  times  up  to  different  divisions 
FIG.  21. — PYK-  with  water  of  known  temperature,  and  then 
NOMETER.  weighing.  The  liquid  under  investigation  is  then 

placed  in  the  apparatus,  and  this  is  weighed 
after  the  positions  of  the  menisci  in  the  capillaries  have  been 
observed;  from  the  data  thus  obtained  the  specific  gravity  can  be 
calculated. 

2.  The  rotation  of  the  plane  of  polarization  is  another  constant  of 
importance. 

Some  substances,  such  as  turpentine,  a  solution  of  sugar,  etc., 
have  the  property  of  rotating  out  of  its  original  position  the  plane 
of  a  ray  of  polarized  light  passing  through  them.  This  phenomenon 
is  called  the  rotation  of  the  plane  of  polarization,  and  substances  pos- 
sessing this  property  are  said  to  be  optically  active.  Polarimetcrs 
have  been  constructed  for  measuring  the  angle  through  which  the 
plane  of  polarization  has  been  rotated  by  an  optically  active  sub- 
stance: of  these  LAURENT'S  (Fig.  22)  is  one  of  the  best  known.  The 
yellow  sodium-light  of  the  burner  TT  is  polarized  in  the  part  of  the 
apparatus  marked  BD,  and  then  passes  through  a  tube  of  known 
length  (200-500  mm.)  placed  in  the  channel  L.  This  tube  contains 
the  liquid  or  solution  under  examination.  The  part  OC  of  the  appa- 
ratus serves  to  measure  the  rotation  of  the  plane  of  polarization. 

The  extent  to  which  the  plane  of  polarization  is  rotated  is  pro- 
portional to  the  length  of  the  tube,  and  is  variously  expressed.  The 
rotation  of  a  substance  can  be  stated,  for  example,  in  terms  of 
the  effect  produced  by  a  given  length  of  the  tube  described.  The 
angle  of  rotation  is  read  off  directly  from  the  instrument,  and  is 
usually  denoted  by  a.  By  convention,  the  specific  rotatory  power 
is  defined  as  the  quotient  obtained  by  dividing  a  by  the  product  of 


2C]  rOLARIMETRY.  33 

the  length  of  the  tube  into  the  specific  gravity  of  the  liquid.     This 
value  is  denoted  by  [a]  so  that 


where  I  is  the  length  of  the  tube,  and  d  the  specific  gravity  of  the 
liquid.  Under  these  conditions,  [a]  expresses  the  rotatory  power  of 
a  substance  per  unit  length  of  the  tube  (1  decimetre),  and  for  unit 
weight  of  the  substance  divided  into  the  unit  of  volume. 


FIG.  22. — LAURENT'S  POLARIMETER. 

The  extent  of  the  rotation  is  dependent  on  the  colour  of  the 
light.  The  measurement  is  often  carried  out  with  sodium-light, 
which  gives  a  yellow  line  in  the  spectroscope,  denoted  by  D.  This 
is  expressed  by  the  symbol  [a]D. 

When  the  rotatory  power  of  a  substance  is  small,  or  when,  on 
account  of  its  slight  solubility,  it  can  only  be  obtained  in  dilute  solu- 
tion, the  rotation  can  often  be  increased  by  adding  a  solution  of 
boric  acid,  molybdic  acid,  uranium  salts,  or  other  substances. 
These  bodies  combine  with  the  organic  substances  to  form  com- 
pounds of  much  higher  rotatory  power. 

The  determination  of  the  refractive  power  or  refraction  of  liquid 
compounds  is  of  great  importance  in  organic  research.  A  descrip- 
tion of  the  apparatus  employed  is  given  in  text-books  of  physics. 
The  index  of  refraction,  n,  depends  on  the  colour  of  the  light 


34  ORGANIC  CHEMISTRY.  [§  27 

employed,  and  is  generally  determined  for  the  three  principal  lines 
of  the  hydrogen  spectrum,  or  for  the  yellow  sodium  line.  The 
difference  in  refraction  for  the  various  colours  is  called  dispersion, 
and  also  finds  application  in  organic  investigation. 

The  refraction  also  depends  on  the  temperature,  and  on  the 
specific  gravity  of  the  liquid.  On  theoretical  grounds,  LORENTZ,  of 
Leyden,  and  LORENZ,  of  Copenhagen,  have  proved  the  expression 

n2-!     !_ 
,  rc2+2  *  d 

<•  to  be  independent  of  the  temperature,  d  representing  the  specific 
gravity,  a  result  fully  supported  by  numerous  experimental  deter- 
minations. The  product  of  this  expression  by  the  molecular 
weight  M, 

n-l        M 


is   called  the   molecular  refraction.     Reference  will  be  made  sub- 
sequently to  the  great  importance  of  this  constant. 

The  molecular  electric  conductivity  is  considered  in  87. 

CLASSIFICATION   OF   ORGANIC   COMPOUNDS. 

27.  The  organic  compounds  are  usually  classed  in  two  main 
divisions.  One  of  these  includes  the  fatty  or  aliphatic  com-. 
pounds  (aAei0o:p,  fat),  and  the  other  the  cyclic  or  ring  compounds. 
The  first  class  owes  its  name  to  the  fact  that  the  animal  and 
vegetable  fats  belong  to  it.  They  are  also  called  hormathic 
compounds,  their  carbon  atoms  being  arranged  in  a  chain  or 
row.  The  name  of  the  second  class  is  derived  from  its  contain- 
ing compounds  in  which  the  presence  of  a  closed  chain  or  ring 
of  atoms  must  be  assumed. 

The  aliphatic  compounds  can  be  regarded  as  derived  from 
methane,  CH4.  The  most  important  cyclic  derivatives  are  the 
aromatic  compounds,  so-called  because  many  of  them  are  char- 
acterized by  an  agreeable  smell  or  aroma. 

It  will  be  shown  later  that  there  are  important  differences 
between  the  general  properties  of  these  two  classes  of  compounds. 


FIRST    PART. 

THE    ALIPHATIC    COMPOUNDS. 


SATURATED  HYDROCARBONS. 

28.  The  aliphatic  compounds  are  defined  in  27  as  those  derived 
from  methane,  CH4.  It  is,  therefore,  advisable  to  begin  the  study 
of  these  compounds  with  this  hydrocarbon. 

Methane  occurs  in  nature  in  the  gases  evolved  from  volcanoes. 
It  escapes  in  coal-mines  during  the  working  of  the  coal-seams,  and 
is  called  fire-damp  by  the  miners.  It  is  also  called  marsh-gas, 
being  present  in  the  gases  evolved  from  marshes  by  decay  of  vege- 
table matter.  It  is  an  important  constituent  of  coal-gas,  being 
present  to  the  extent  of  30-40  per  cent. 

It  can  be  obtained  by  the  following  methods. 

1.  By  SABATIER  and  SENDERENS'S  synthesis.  When  a  mixture 
of  hydrogen  and  carbon  monoxide  is  passed  over  reduced  nickel 
at  250°-300°,  methane  is  formed: 


The  nickel  undergoes  no  apparent  change,  and  can  be  used  re- 
peatedly. At  a  temperature  of  230°-300°,  carbon  dioxide  reacts 
similarly  with  hydrogen  in  presence  of  finely-divided  nickel: 

CO2  +  4H2  =  CH4  +  2H2O. 

2.  Methane  can  also  be  synthesized  directly  from  its  elements 
by  passing  hydrogen  through  a  heated  tube  containing  reduced 
nickel  mixed  with  very  finely-divided  carbon  obtained  by 
previously  decomposing  methane.  An  equilibrium  is  attained, 
corresponding  at  475°  and  one  atmosphere  with  51  per  cent,  of 
methane  : 


35 


'36  ORGANIC  CHEMISTRY.  [§  29 

PRING  has  found  that  pure  carbon  and  pure  hydrogen  also 
combine  directly  without  a  catalyst  at  temperatures  above 
1100°,  the  equilibrium  at  1200°  corresponding  with  about  0-35 
per  cent,  of  methane. 

3.  By  the  action  of  water  on  aluminium  carbide: 


Other  methods  of  preparation  are  referred  to  in  75  and  83. 

Physical  and  Chemical  Properties.  —  Methane  is  an  odour- 
less and  colourless  gas  of  sp.  gr.  0*559  (air  =  l).  Its  critical 
pressure  is  55  atmospheres,  and  its  critical  temperature  —82°. 
It  boils  at  -  165°,  and  solidifies  at  -  186°.  It  is  only  slightly 
soluble  in  water,  but  more  so  in  alcohol.  It  is  decomposed  into 
carbon  and  hydrogen  by  the  sparks  of  an  induction-coil,  or  in 
the  electric  arc.  Oxidizing  substances,  such  as  nitric  and  chromic 
acids,  do  not  attack  it,  or  only  very  slightly,  while  concentrated 
sulphuric  acid  and  strong  alkalis  have  no  action  upon  it.  It 
burns  with  an  almost  non-luminous  flame.  When  mixed  with 
.air  or  oxygen  it  forms  a  violently  explosive  mixture,  the  reaction 
being  in  accordance  with  the  equation 

CH4-f2O2  =  CO24-2H2O. 

This  so-called  "fire-damp"  is  the  cause  of  the  explosions  which 
sometimes  occur  in  coal-mines.  Chlorine  and  bromine  react  with 
methane,  replacing  its  hydrogen  atoms  by  halogen  atoms,  and 
forming  a  hydrogen  halide  : 

CH4+2C1  =  CH3C1  +  HC1. 

The  replacement  of  one  atom  by  another  is  called  substitution. 
If  chlorine  or  bromine  is  present  in  excess,  the  final  product  is 
CC14  or  CBr4. 

29.  There  exists  a  series  of  hydrocarbons  having  general  chem- 
ical properties  similar  to  those  of  methane.  Examples  of  these 
compounds  are  ethane  C2H6,  propane  C3Hs,  butane  C4Hjo,  pen- 
tane  C5H12,  hexane  C6H14,  etc.,  pentatriacontane  CssH^,  and  hexa- 
contane  C6oHi22.  These  formula?  can  be  summed  up  in  the  general 
expression  CnH2n+2:  for  methane,  n=l.  The  hydrocarbons 
CnH2n+2  resemble  methane  in  their  power  of  resisting  oxidation, 


§  30]  PARAFFINS.  37 

and  are  unacted  on  by  concentrated  sulphuric  acid,  while  halogens 
act  on  them  with  substitution  of  hydrogen  and  formation  of 
compounds  CnH2n+1Cl,  CnH2nCl2,  and  so  on. 

The  higher  hydrocarbons  can  be  obtained  by  building-up 
from  those  lower  in  the  series.  For  example,  ethane  is  got  from 
methane  by  replacement  of  a  hydrogen  atom  by  halogen,  and 
treatment  of  the  halide  thus  obtained  with  sodium  or  calcium: 

2CH3I  +  Na2  =  C2H6 + 2NaI . 

Propane  can  be  prepared  in  accordance  with  tne  following  equa- 
tion: 

CH3I  +  C2H5I  +  Na2  =  C3H8 + 2NaI : 

and,  in  general,  CnH2n+2  is  obtained  by  the  action  of  sodium  upon 
CmH2m+iI-hCpH2p+1I,  when  m+p=n. 

In  addition  to  propane,  butane,  C4H10,  is  formed  from  2C2H6I, 
and  ethane,  C2H6,  from  2CH3I,  three  hydrocarbons  being  obtained. 
This  is  always  so  in  such  syntheses. 

Since  methane  can  be  prepared  synthetically,  it  is  evidently 
possible  to  synthesize  each  hydrocarbon  of  the  formula  CnH2n+2. 

30.  Nomenclature. — The  hydrocarbons  CnH2n+2  are  always 
denoted  by  the  termination  "ane."  The  first  four  members, 
methane,  ethane,  propane,  and  butane,  have  special  names:  the 
others  are  denoted  by  the  Greek  or  Latin  numeral  corresponding 
with  the  number  of  carbon  atom;.  Thus  C8Hi8  is  called  octane, 
Ci2H26  dodecane,  C3iH64  hentriacontane,  and  so  on. 

It  will  often  be  necessary  to  consider  groups  of  atoms  un- 
obtainable in  the  free  state,  but  theoretically  derivable  by  re- 
moval of  a  hydrogen  atom  from  the  hydrocarbons  CnH2n+2. 
These  groups  have  the  general  formula  CnH2n+1,  and  are  called 
alkyl-groups.  They  are  denoted  individually  by  changing  the 
termination  "ane"  of  the  corresponding  hydrocarbon  into  "yl." 
Thus  CH3  is  called  methyl,  C2H5  ethyl,  C3H7  propyl,  C4H9  butyl, 
Ci2H25  dodecyl,  etc. 

The  hydrocarbons  CnH2n+2  have  the  general  name  saturated 
hydrocarbons,  because  they  are  saturated  with  hydrogen;  that  is, 
are  unable  to  take  up  any  more  hydrogen  atoms  into  the  molecule. 
They  are  also  called  paraffins,  because  paraffin-wax  consists  of  a 


38  ORGANIC  CHEMISTRY.  [§31 

mixture  of  the  higher  members.  The  word  paraffin  is  derived 
from  parum  affinis,  and  indicates  the  stability  of  this  substance 
towards  chemical  reagents. 

31.  Occurrence  in  Nature. — The  hydrocarbons  CnH2n+2  occur 
in  nature  in  enormous  quantities.  Crude  American  petroleum 
consists  of  a  mixture  of  a  great  number  of  these  compounds,  from 
the  lowest  to  the  highest  members  of  the  series.  Three  principal  pro- 
ducts are  obtained  from  this  petroleum  by  fractional  distillation,  after 
treatment  with  acids  and  alkalis  to  free  itfromsubstances  other  than 
hydrocarbons  of  the  formula  CnH2n  +  2-  The  most  volatile  por- 
tion is  called  light  petroleum,  petroleum-ether,  benzine,  naphtha,  or 
ligrom:  it  distils  between  40°  and  150°,  and  contains  lower  mem- 
bers, chiefly  C6H14,  C7H16,  and  C8H18.  It  is  extensively  employed 
as  motor-spirit,  as  a  solvent  for  fats,  oils,  and  resins,  and  in  the 
removal  of  stains  from  clothing  in  the  "  dry-cleaning  process." 

The  portion  distilling  between  150°-300°  is  ordinary  petroleum^ 
ar>d  is  used  on  a  large  scale  for  lighting  and  cooking. 

The  danger  involved  in  its  use  is  by  no  means  small,  a  large  num- 
ber of  accidents  by  fire  being  attributable  to  this  source.  The  fact 
that  fires  are  often  caused  by  the  overturning  of  petroleum-lamps 
is  traceable  to  the  presence  in  the  petroleum  of  a  part  of  the  more 
volatile  products,  and  to  their  vapour  producing  an  inflammable 
mixture  with  air.  When  a  lamp  filled  with  petroleum  freed  by 
careful  fractionation  from  constituents  of  low  boiling-point,  is  upset, 
the  flame  is  extinguished.  Petroleum  thus  purified  is  a  commercial 
product. 

To  ascertain  whether  a  sample  of  petroleum  contains  these  more 
volatile  products,  its  -flash-point  is  determined  by  heating  it  slowly 
in  a  specially  constructed  apparatus,  devised  by  Sir  FREDERICK  ABEL, 
and  observing  the  temperature  at  which  the  mixture  of  vapour  and 
air  over  the  petroleum  can  just  be  ignited.  Experience  has  shown 
that  there  is  no  danger  with  a  flash-point  of  40°  C.  (104°  F.).  Large 
quantities  of  petroleum  come  into  the  market  with  a  flash-point  of 
22°-24°  C.  (72°-75°  F.):  they  are  the  cheaper  kinds,  are  used  by 
the  largest  proportion  of  the  population,  and  constitute  a  great 
source  of  danger  from  fire.  It  would  be  very  advantageous  if  the 
law  insisted  upon  a  flash-point  of  about  40°  C.  or  104°  F.,  as  has 
already  been  done  in  some  countries. 

Further  distillation  above  300°  yields  lubricating  oil,  and  then 
wax-like  products,  the  residue  in  the  still  ultimately  carboniz- 
ing. The  residual  product  from  the  evaporation  of  American. 


§  32]  PETROLEUM.  39 

petroleum  in  the  air  is  called  "  vaseline  "  or  petroleum-  jelly. 
It  is  semi  -solid  at  ordinary  temperatures,  white  when  pure,  and 
and  finds  application  in  pharmacy  as  a  substitute  for  fats  in 
the  preparation  of  ointments.  It  is  employed  as  a  lubricant 
for  machinery,  and  also  for  covering  the  surfaces  of  metallic 
articles  to  hinder  oxidation.  As  a  protective  coating  it  is  superior 
to  vegetable  and  animal  fats,  which  become  rancid  in  course  of 
time,  and  thus  attack  the  surface  of  the  metal.  Vaseline  is 
free  from  acid,  and  remains  unchanged  by  exposure  to  air. 

Paraffin-wax  is   a  mixture   of  the   highest   members   of  the 
series  CnH2n+2,   among  them  the  hydrocarbons  C22H46,  C24H50, 


Some  kinds  of  crude  petroleum,  notably  that  obtained  from 
Java,  contain  considerable  quantities  of  these  highest  members. 
They  are  present  in  but  small  amount  in  American  petroleum. 
Liquid  paraffin  is  a  product  of  high  boiling-point,  obtained  in 
the  dry  distillation  of  brown  coal.  Earth-wax  or  ozokerite,  occurs  in 
Oalicia,  and  consists  chiefly  of  paraffin-wax.  This  substance  is  also 
obtained  in  the  dry  distillation  of  the  brown  coal  found  in  Saxony. 
Asphalt  is  an  oxidation-product  of  the  higher-boiling  con- 
stituents of  petroleum.  On  prolonged  heating  at  a  high  tem- 
perature in  the  air,  paraffin-wax  also  absorbs  oxygen  and  becomes 
dark  in  colour. 

32.  The  petroleum  stored  in  the  interior  of  the  earth  at  depths 
up  to  600  metres  has  probably  been  formed  from  fats  under  the 
influence  of  high  temperature  and  great  pressure.  In  confirma- 
tion of  this  hypothesis,  ENGLER  has  prepared  by  distillation  of 
train-oil  under  pressure  a  liquid  very  similar  to  natural  petroleum. 
The  parent  fats  may  have  had  either  a  vegetable  or  an  animal  origin. 
There  appears  to  be  no  genetic  interdependence  between  the 
occurrence  of  the  enormous  deposits  of  fossilized  vegetable  remains 
constituting  coal,  brown  coal,  and  so  on,  and  that  of  petroleum, 
since  coal-fields  and  petroleum-wells  are  found  in  districts  far  apart. 
This  fact  constitutes  a  powerful  argument  in  favour  of  the  theory 
of  the  animal  origin  of  the  fats  from  which  petroleum  has  been 
formed;  although  a  possible  explanation  is  the  formation  of  petro- 
leum and  coal  during  different  geological  periods. 

The  hypothesis  explaining  the  formation  of  petroleum  as  a 
result  of  the  interaction  of  water  and  certain  metallic  carbides  is 
rendered  extremely  improbable  by  two  facts:  (1)  almost  every  variety 
of  petroleum  is  optically  active,  an  indication  of  its  derivation 
from  optically  active  organic  material  (223)  ;  (2)  petroleum  is  never 


40  ORGANIC  CHEMISTRY.  [§  33 

found  in  the  oldest  geological  formations,  but  only  in  those  in  which 
the  presence  of  vegetable  and  animal  remains  has  been  demonstrated. 

Homologous  Series. 

33.  Each  of  the  hydrocarbons  CnH2n+2  differs  in  composition 
from  the  rest  by  nXCH2,  as  the  general  formula  shows.  It  was 
pointed  out  (29)  that  this  difference  exercises  but  slight  influence 
on  their  chemical  properties. 

Whenever  organic  compounds  show  great  resemblance  in  their 
chemical  properties,  and  have  at  the  same  time  a  difference  in 
composition  of  ftXCH2,  they  are  said  to  be  homologous  (6/xoA.oyos, 
corresponding),  the  name  homologous  series  being  given  to  such. 
a  group  of  compounds.  As  will  be  seen  later,  many  of  these- 
series  are  known. 

It  is  easy  to  understand  how  much  this  simplifies  the  study  of 
organic  chemistry.  Instead  of  having  to  consider  the  chemical 
properties  of  each  compound  individually,  it  is  sufficient  to  do  so- 
far  one  member  of  a  homologous  series,  as  this  gives  the  principal 
characteristics  of  all  the  other  members.  In  addition  to  tha 
main  properties  common  to  the  members  of  a  homologous  series, 
each  individual  member  has  its  characteristics.  Except  in  a  few- 
instances,  this  book  will  not  deal  with  the  latter,  because  they 
only  need  to  be  considered  in  a  more  extensive  survey  of  the  sub- 
ject. 

The  physical  properties,  such  as  the  melting-points  and 
boiling-points,  specific  gravities,  and  solubilities,  of  the  members 
of  a  homologous  series,  generally  change  uniformly  as  the  number 
of  carbon  atoms  increas3s.  In  general  it  may  be  said  that  the 
melting-points  and  boiling-points  rise  from  the  lower  to  the  higher 
members  of  a  homologous  series. 

A  table  of  some  of  the  physical  constants  of  a  number  of 
normal  (36)  members  of  the  paraffin  series  is  given  on  p.  41. 

An  inspection  of  this  table  reveals  that  the  first  four  members 
are  gases  at  the  ordinary  temperature,  those  from  Cs  to  GIG  liquids, 
and  the  higher  members  solids.  Although  methane  is  odourless, 
the  liquid  members  have  a  characteristic  petroleum-like  smell; 
the  solid  members,  on  the  other  hand,  are  odourless.  All  are 
nearly  insoluble  in  water. 

It  should  be  further  remarked  that  the  differences  between  the 
melting-points  and  boiling-points  respectively  of  successive  mem- 


HOMOLOGOUS   SERIES. 


41 


bers  of  the  series  become  smaller  with  increase  in  the  number  of 
carbon  atoms.  This  phenomenon  is  usually  found  in  homologous 
series. 


For- 
mula. 

Name. 

Melting- 
point. 

Observed 
Boiling- 
point, 

Calculat'd 
Boiling- 
point. 

Specific  Gravity, 

CH4 

Methane 

-186° 

-160° 

-166.3° 

0-415  (at  -160°) 

C2H6 

Ethane 

-172.1° 

-    93° 

-  95-3° 

0-446  (at  0°) 

C3H8 

Propane 



-  45° 

-  43-1° 

0-536  (atO°) 

C«H10 

Butane 

-135° 

-  0.1° 

-     0.4° 

0-600  (at  0°) 

C5H12 

Pentane 

-130.8° 

36.3° 

36-4° 

0-627  (at  14°) 

CH 

Hexane 

-  94.03° 

68-9° 

68-9° 

0-658  (at  20°) 

C7H16 

Heptane 

-  97.1° 

98-4° 

98-3° 

0-683    "     " 

€8H18 

Octane 

-  56-5° 

125-6° 

125.1° 

0-702    "     " 

CqHgfl 

Nonane 

-  51° 

149-5° 

149-8° 

0-718    "    " 

CTJ 
lo*1^ 

Decane 

-  31° 

173° 

172-8° 

0-730    "    " 

C,,l£ 

CijHjj 

Undecane 
Dodecane 

-  26° 
-   12° 

194° 
214-5° 

194-3° 
214-6° 

0-774  at  melting-point 
0-773  " 

C'uHaO 

Tetradecane 

4° 

252-5° 

252-0° 

0-775  " 

C16H34 

Hexadecane 

18° 

287-5° 

285-9° 

0-775  " 

C»H« 

Eicosane 

36-5° 

205°* 



0-7775" 

C2,  H44 

Heneicosane 

40-1° 

215° 



0-7778" 

C^H^ 

Tricosane 

47-4° 

234° 

'. 

0-7799" 

Cj,iHM 

Hentriacontane 

68-4° 

302° 



0-7799" 

^3oH72 

Pentatriacontane 

74° 

331° 



0-7813"               " 

Q»Hm 

Hexacontane 

101° 

~ 

*  At  15  mm.  pressure,  and  the  same  for  those  following. 

For  the  boiling-points  these  differences  are  functions  of  the  ab- 
solute temperature.  SYDNEY  YOUNG  has  induced  the  empirical 
formula 


144-86 


~~ 


giving  the  difference  in  boiling-point  of  two  successive  members  of 
the  series,  when  T  is  the  boiling-point  on  the  absolute  scale  of  the 
more  volatile  of  the  two  homologues.  The  boiling-points  in  the 
fifth  column  of  the  table  in  this  section  were  calculated  by  the  aid 
of  this  formula. 

The  expression  holds  not  only  for  this  homologous  series  of 
hydrocarbons,  but  also  for  many  other  homologous  series.  The  dif- 
ferences between  the  calculated  and  observed  boiling-points  are 
greatest  for  the  lower  members.  For  some  homologous  series  the 
divergences  are  considerable,  but  can  usually  be  proved  to  be 
due  to  association  of  the  molecules  of  the  compound  in  the  liquid 
state;  that  is,  the  molecular  weight  in  this  condition  is  twice,  or  a 
higher  multiple  of,  that  in  the  normal  gaseous  state. 


42  ORGANIC  CHEMISTRY.  [§34 

YOUNG'S  formula  holds  for  normal  pressure,  760  mm.  For  the 
absolute  boiling-points  of  two  substances  a  and  6  the  simple  relation 

T*JF* 

Tb     T'b 

often  obtains,  T  and  T'  being  the  absolute  boiling-points  of  the 
•      substances  at  the  same  arbitrary  pressure.     Otherwise  expressed, 
this  equation  means  that  the  ratio  of  the  boiling-points  at  different 
pressures  is  often  constant. 

\ 
Isomerism  and  Structure. 

'  34.  Only  one  substance  with  the  formula  GEL*  is  known :  it 
is  methane.  Similarly,  there  is  only  one  compound  having  the 
formula  C2H6,  and  one  with  the  formula  CsHg.  There  are  known, 
however,  two  compounds  with  the  formula  C4Hio,  three  with 
the  formula  C5H]2,  five  with  the  formula  C6H14,  and  so  on.  The 
phenomenon  of  two  or  more  compounds  being  represented  by  one 
formula  is  called  isomerism  (2),  and  compounds  having  the  same 
formula  are  called  isomerides.  Jsomerism  is  explained  by  a  con- 
sideration of  the  grouping  of  the  atoms  in  the  molecule. 

One  of  two  hypotheses  may  be  adopted.  In  the  first  place,  the 
arrangement  of  the  atoms  may  be  regarded  as  continually  chang- 
ing, a  molecule  being  represented  as  like  a  planetary  system,  the 
configuration  of  which  changes  from  moment  to  moment.  This 
hypothesis,  however,  cannot  explain  the  phenomenon  of  isomerism. 
For  example,  it  is  not  apparent  how  the  four  carbon  atoms  and 
ten  hydrogen  atoms  in  butane  could  form  two  different  substances 
if  the  arrangement  were  indeterminate,  for  there  are  trillions 
of  molecules  present  in  even  one  cubic  millimetre,  and  all  the 
possible  configurations  of  these  fourteen  atoms  must  therefore 
be  supposed  to  exist  at  any  instant. 

Isomerism  can  at  once  bo  understood  by  assuming  a  definite 
and  unchanging  arrangement  of  the  atoms  in  the  molecule,  be- 
cause the  difference  in  the  properties  of  isomeric  compounds  may 
be  then  explained  by  a  difference  in  the  arrangement  of  equal 
numbers  of  the  same  atoms. 

A  definite  and  unchanging  arrangement  of  the  atoms  in  a  mole- 
cule does  not  involve  their  being  immovable  with  respect  to  one 
another.  For  example,  they  might  revolve  round  a  point  of 
equilibrium  without  alteration  in  their  order  of  succession. 


1SOMER1SM   AND  STRUCTURE  43 

35.  Since  the  phenomenon  of  isomerism  leads  to  the  assump- 
tion of  a  definite  arrangement  of  the  atoms  in  the  molecule,  it  is 
necessary  to  solve  the  problem  of  how  the  atoms  in  the  molecules 
of  different  compounds  are  arranged.  The  basis  of  the  solution 
is  the  quadrivalency  of  the  carbon  atom.  In  methane  the  arrange^ 
ment  of  the  atoms  may  be  represented  by  the  formula 

/H 

C<H' 
\H 

in  which  the  four  linkings  of  the  carbon  atom  act,  as  it  were, 
like  four  points  of  attraction,  each  holding  a  univalent  hydrogen 
atom  fast.  This  is  the  only  possibility,  because  the  hydrogen 
atoms  cannot  be  bound  to  one  another,  the  only  point  of  at- 
traction, or  single  linking,  of  each  being  already  in  union  with 
one  of  the  linkings  of  the  carbon*  atom. 

The  arrangement  of  the  atoms  in  ethane,  CyEI6,  must  now 
be  investigated.  This  substance  can  be  obtained  by  the  action 
of  sodium  upon  methyl  iodide,  CH3T  (53),  with  a  quadrivalent 
carbon  atom,  three  univalent  hydrogen  atoms,  and  one  univalent 
iodine  atom.  It  must  therefore  be  represented  thus: 

H 


Sodium  reacts  with  methyl  iodide  by  withdrawing  the  iodine 
atoms  from  two  molecules,  with  formation  of  ethane.  The  re- 
moval of  the  iodine  atom  has  the  effect  of  setting  free  the  carbon 
linking  previously  attached  to  this  atom,  with  the  production  of 
two  groups 


H/ 

Since  the  formula  of  ethane  is  C2H6,  it  is  evident  that  the  only 
possible  arrangement  of  its  atoms  is  that  having  the  two  free 
linkings  of  the  methyl-groups  united  to  one  another: 

H  H 


-—          . 
H/         \H 


44  ORGANIC  CHEMISTRY.  [§35 

The  arrangement  of  the  atoms  in  propane  can  be  determined 
in  an  exactly  analogous  manner.  It  was  mentioned  (29)  that 
propane  is  formed  by  the  action  of  sodium  on  a  mixture  of  methyl 
and  ethyl  halides.  Since  ethane  can  be  prepared  by  the  action 
of  sodium  on  methyl  iodide,  the  formula  of  an  ethyl  halide  can 
only  be 

H 


-  , 

H/         \X 

•where  X  represents  a  halogen  atom. 

If  the  halogen  is  taken  away  from  this  substance  and  from 
methyl  iodide  simultaneously,  the  residues  unite,  showing  that 
propane  has  the  structure 

H 

H\        '        /H 
H-^C—  0—  C^-H, 

H 
or  shortly  H3C.CH2-CH3. 

Such  an  arrangement  of  symbols  expressing  the  configuration 
jk  molecule,  and  indicating  the  form  or  structure,  is  called  a 
structural  or  constitutional  formula. 

The  following  example  makes  it  clear  how  cases  of  isomer- 
ism  can  be  explained  by  differences  in  structure.  One  of  the  five 
known  hexanes  boils  at  69°,  and  has  a  specific  gravity  of  0-6583 
at  20-9°:  another  boils  at  58°,  and  has  a  specific  gravity  of  0-6701 
at  17-5°.  The  first  is  obtained  by  the  action  of  sodium  on  normal 
propyl  iodide,  CHs-CIVC^I.-  From  the  foregoing  it  follows 
that  this  hexane  must  have  the  structure 

CHs  •  CH2  •  CH2  —  CH2  •  CH2  •  CHs. 

It  is  named  dipropyl,  on  the  assumption  that  it  has  been  formed 
by  the  union  of  two  propyl-groups. 

In  addition  to  this  normal  propyl  iodide,  an  isomeride  called 
isopropyl  iodide  is  known.  Both  compounds  can  be  readily 
converted  into  propane,  CH3-CH2-CH3.  Assuming  that  the 
isomerism  is  due  to  a  different  arrangement  of  the  atoms  in  the 
molecule,  it  follows  that  the  isomerism  of  the  two  compounds 
can  only  be  explained  by  a  difference  in  the  position  occu- 


§36] 


CARBON  CHAINS.  45 


pied  by  the  iodine  atom  in  the  molecule,  because  the  arrangement 
of  the  atoms  in  propane  is  known,  and  the  propyl  iodides  only 
differ  from  propane  in  having  one  of  the  hydrogen  atoms  in  the 
latter  replaced  by  iodine.  isoPropyl  iodide  must  therefore  have 

the  structure 

H 


if  the  constitution  of  normal  propyl  iodide  is  CH3«CH2-CH2l. 

The  hexane  boiling  at  58°  is  produced  by  the  action  of  sodium 
on  ^sopropyl  iodide,  and  consequently  must  have  the  structure 

CHa-OH-CH,  CH  CH3 

H.CH  CH3>(  <CH3' 


Hence  it  is  called  diisopropyl. 

Carbon  Chains. 

36.  The  foregoing  facts  evidently  make  it  reasonable  to  assume 
the  existence  of  a  bond  between  carbon  atoms  in  the  molecules 
of  organic  compounds.  This  bond  is  a  very  strong  one,  since  the 
saturated  hydrocarbons  resist  the  action  of  powerful  chemical 
reagents  (29).  The  property  possessed  by  carbon  atoms  of  com- 
bining to  form  -a  series  of  many  atoms,  a  carbon  chain,  like  that 
in  the  hexanes  above  described,  furnishes  a  marked  distinction 
"between  them  and  the  atoms  of  all  the  other  elements  which 
•either  have  not  this  power,  or  have  it  only  in  a  very  inferior  de- 
gree. The  fact  that  the  number  of  carbon  compounds  is  so 
enormous  is  due  to  this  property,  in  conjunction  with  the  quadri- 
valency  of  the  carbon  atom. 

A  carbon  chain  like  that  in  dipropyl  is  said  to  be  normal. 
On  the  other  hand,  an  example  of  a  branched,  chain  is  fur- 
nished by  diisopropyl.  Each  carbon  atom  in  the  normal  chain 
is  linked  directly  to  not  more  than  two  others:  in  branched 
chains  there  are  carbon  atoms  directly  linked  to  three  or  four 
others.  A  normal-chain  compound  is  usually  denoted  by  putting 
n  before  its  name;  branched-chain  compounds  are  often  dis- 
tinguished by  the  prefix  iso. 


46  ORGANIC  CHEMISTRY.  [§37 

A  few  other  definitions  may  find  a  place  here.  A  carbon  atom 
linked  to  only  one  other  carbon  atom  is  called  primary;  if  linked 
to  two  carbon  atoms  it  is  named  secondary;  if  to  three,  tertiary; 
if  to  four,  quaternary.  A  carbon  atom  situated  at  the  end  of 
a  chain  is  called  terminal.  The  carbon  atoms  of  a  chain  are  dis- 
tinguished by  numbers,  the  terminal  one  being  denoted  by  1, 
the  one  next  it  by  2,  and  so  on ;  for  example, 

/^ITT       /^TJ       OtT       OUT 

vAtJ.3  •  \jL\-2  *  ^-n-2  *  vAtl-3* 

1  2  3       '     4 

Sometimes  the  terminal  atom  is  denoted  by  a,  the  one  linked  to 
it  by  /?,  and  the  succeeding  one  by  /-,  etc.,  but  a  terminal  C-atom 
in  a  CN-group,  CHO-group,  or  COOH-group,  is  distinguished  by 
n»,  the  next  by  a,  and  so  on. 

Law  of  the  Even  Number  of  Atoms. — The  number  of  hydrogen 
atoms  in  the  saturated  hydrocarbons  is  even,  since  their  formula 
is  CnH2n+3.  All  other  organic  compounds  may  be  regarded  as 
derived  by  exchange  of  these  hydrogen  atoms  for  other  elements 
or  groups  of  atoms,  or  by  the  removal  of  an  even  number  of 
hydrogen  atoms,  or  by  both  causes  simultaneously.  From  this  it 
follows  that  the  sum  of  the  atoms  with  uneven  valency  (hydrogen, 
the  halogens,  nitrogen,  phosphorus,  etc.)  must  always  be  an  even 
number.  The  molecule  of  a  substance  of  the  empirical  composition 
C3H2O2N  must  be  at  least  twice  as  great  as  this,  because  2H-HN 
is  uneven. 

Number  of  Possible  Isomerides. 

37.  The  quadrivaleney  of  the  carbon  atom,  coupled  with  the 
principle  of  the  formation  of  chains  of  atoms,  not  only  explains 
the  existence  of  the  known  isomerides,  but  also  renders  possible 
the  prediction  of  the  existence  of  unknown  compounds.  Thus 
for  a  compound  C4Hi0  either  the  structure  CH3-CH2-CH2-CH3  or 

£53>CH-CH3  may  be  assumed,  and  there  are  no  further  possi- 
bilities. Pentane  may  have  the  following  structural  formulae: 

(1)  CH3.CH2.CH2.CH2.CH3;     (2)  CH3.CH 

^013' 
3 \  p  ^^Ji  3 
W  CH3>C<CH3- 


[§37  NUMBER  OF  POSSIBLE   I  SO  ME  RIDES.  47 

For  hexane  the  following  five  are  possible: 

Q)  CH3-CH2.CH2.CH2.CH2.CH3;  (2)  CH3.CH2.CH2.CH<^3; 

(3)  CH3.CH2.CH.CH2-CH3;     (4)  CH3.CH.CH.CH3; 
CH3  CH3  CH3 

/CH3 

(5)  CH3.CH2.C^CH3. 
XCH3 

Jf  the  principles  given  above  be  assumed,  it  will  be  impossible  to 
find  structural  formulae  other  than  those  mentioned. 

Should  it  be  possible  actually  to  obtain  the  same  number  of 
isomerides  as  can  be  thus  predicted,  and  no  more,  and  should  the 
products  of  synthesis  or  decomposition  of  any  existing  isomeride 
necessitate  the  assumption  of  the  same  structural  formula  as  that 
required  by  the  theory,  these  facts  constitute  a  very  important 
confirmation  of  the  correctness  of  the  principles  upon  which  the 
theory  is  based.  This  correspondence  of  fact  with  theory  has  been 
proved  to  hold  good  in  many  instances,  and  therefore,  on  the  other 
hand,  affords  an  important  means  of  determining  the  structure  of 
a  new  compound,  because  if  all  the  structural  formulae  possible 
for  the  compound  according  to  the  theory  are  considered  in  turn, 
one  of  them  will  be  found  to  be  that  of  the  substance. 

Frequently  the  number  of  isomerides  actually  known  is  much 
smaller  than  that  which  is  possible,  because  the  number  of  possible 
isomerides  increases  very  quickly  with  increase  of  the  number 
of  carbon  atoms  in  the  compound.  CAY  LEY  has  calculated  that 
there  are  nine  possible  isomerides  for  C?Hi6,  eighteen  for  CgHig, 
thirty-five  for  CgH20,  seventy-five  for  Ci0H22,  one  hundred  and 
fifty-nine  for  CnH24,  three  hundred  and  fifty-four  for  Ci2H26, 
eight  hundred  and  two  for  Ci3H28,  and  so  on.  Chemists  have  not 
tried  to  prepare,  for  example,  every  one  of  the  eight  hundred  and 
two  possible  isomerides  of  the  formula  C13H28,  because  their  atten- 
tion has  been  occupied  by  more  important  problems.  There  can, 
however,  be  no  doubt  as  to  the  possibility  of  obtaining  all  these 
compounds,  because,  as  mentioned  above,  the  methods  for  build- 
ing them  up  are  known,  and  there  would  therefore  be  no  theoretical 
difficulties  in  the  way  of  these  experiments,  though  there  might 
be  hindrances  of  an  experimental  nature. 


48 


ORGANIC  CHEMISTRY. 


[§38 


Physical  Properties  of  Isomeric  Compounds. 

38.  Of  the  different  isomerides  the  normal  compound  has  the 
highest  boiling-point. 

The  nearer  a  side-chain  is  to  the  terminal  carbon  atom,  the 
more  it  lowers  the  boiling-point.  Two  side-chains  attached  to 
different  carbon  atoms  produce  a  considerable  reduction  in  the 
boiling-point.  The  isomeride  with  two  side-chains  linked  to  the 
penultimate  carbon  atom  has  the  lowest  boiling-point.  The  sub- 
joined table  affords  confirmation  of  these  statements. 


Name. 

Formula. 

Boilinp- 

point. 

n-Octane 
2-»Methylheptane 

CH3-(CH2)6-CH3 
CH3-CH-(CH2)4-CH3 

124-7° 
116-0° 

CH3 

3-Methylheptane 

CH3  •  CH2  •  CH  •  (CH2)3  •  CH3 

117-6° 

CH3 

4^Methylheptane 

CH3  •  (CH2)2  •  CH  •  (CH2)2  •  CH3 

118-0° 

CH3 

2  :  5-Dimethylhexane 

CH3-CH-(CH2)2-CH-CH3 

108-3° 

CH3              CH3 

2  :  2'  :  3  :  S'-Tetramethylbutane 

CH3        CH3 
OH3  •  O  O  •  OH3 

104° 

CH3        CH3 

ALCOHOLS,  CnH2n+20. 

Methods  of  Formation  and  Constitution. 

39.  The  alcohols  of  this  homologous  series  can  be  obtained  by 
the  action  of  silver  hydroxide  on  the  alkyl  halides: 


It  is  usual  to  bring  an  alkyl  iodide  into  contact  with  moist 
oxide  of  silver,  the  portion  dissolved  in  the  water  reacting  like 
silver  hydroxide  ("Inorganic  Chemistry,"  246).  The  preparation 
of  the  alcohol  from  the  iodide  can  also  be  effected  by  heating  it 
with  excess  of  water  at  100°: 


When  sodium  reacts  with  an  alcohol  CnH2n+2O,  one  gramme- 
atom  of  free  hydrogen  is  liberated  from  each  gramme-molecule  of 
the  alcohol,  and  a  compound  called  sodium  alkoxide  (alcoholate)  , 
CnH2n+iNaO,  is  produced:  in  presence  of  excess  of  water  this 
decomposes  into  sodium  hydroxide  and  an  alcohol.  The  sodium 
has  thus  replaced  one  atom  of  hydrogen,  and  neither  it  nor  any 
other  metal  can  replace  more  than  one  hydrogen  atom:  if  excess 
of  sodium  is  added,  it  remains  unacted  upon.  It  follows  that 
only  one  hydrogen  atom  in  the  alcohol  is  replaceable  by  sodium. 

When  an  alcohol  is  treated  with  trichloride  or  pentachlorida 
of  phosphorus,  an  alkyl  chloride  is  formed: 

3CnH2n+20  +  PC13  -  3CnH2n+1  Cl  +  H3P03. 

,  From  these  facts  the  constitution  of  the  alcohols  can  be  in- 
duced. Silver  hydroxide  can  only  have  the  structure  Ag  —  O  —  H, 
its  bivalent  oxygen  atom  being  linked  to  its  univalent  silver  and 
hydrogen  atoms.  When  silver  hydroxide  is  brought  into  contact 
with  an  alkyl  iodide,  the  reaction  must  be  supposed  to  take  place 
so  that  on  the  one  hand  the  iodine  atom  is  set  free  from  the  alkyl- 
group,  and  on  the  other  hand  the  silver  atom  from  the  hydroxyl- 

49 


50  ORGANIC  CHEMISTRY.  [§39 

group.     The  alkyl-group  and  the  hydroxyl-group  are  thus  afforded 
the  opportunity  of  uniting  by  means  of  the  linking  set  free  in  each: 

CnH2n+1  |I  +  Ag|OH  -»  CnH2n+1— OH. 

This  method  of  formation  proves  that  the  alcohols  contain  a 
hydroxyl-group.  Their  preparation  from  alkyl  iodides  and  water 
leads  also  to  the  same  conclusion,  which  is  further  supported  by 
the  two  properties  of  alcohols  mentioned  on  the  last  page.  It  is 
evident  that  if  their  structure  is  expressed  by  CnH2n+l-OH,  all 
the  hydrogen  atoms  present,  except  one,  are  linked  directly  to 
carbon,  while  one  hydrogen  atom  occupies  a  special  position  in  tho 
molecule,  being  attached  to  the  oxygen  atom,  which  is  united 
through  its  second  linking  to  a  carbon  atom.  It  is  only  natural 
to  suppose  that  the  special  position  occupied  by  this  hydrogen 
atom  is  accompanied  by  a  special  property,  that  of  being  the  only 
one  of  all  the  hydrogen  atoms  replaceable  by  alkali-metals.  More- 
over, sodium  sets  free  hydrogen  from  another  compound  con- 
taining .without  doubt  a  hydroxyl-group:  this  compound  is  water, 
for  which  no  other  constitution  is  possible  than  H — O — H. 

The  fact  that  the  alcohols  are  converted  into  alkyl  chlorides 
by  the  action  of  the  chlorides  of  phosphorus  is  additional  proof 
that  they  contain  a  hydroxyl-group.  The  empirical  formulae 
CnH2n+2O  and  CnH2n+]X  show  that  the  halogen  has  replaced 
OH.  It  may  be  assumed  that  in  this  reaction  the  hydroxyl  of 
the  alcohol  has  changed  places  with  the  chlorine  of  the  phosphorus 
compound:  "^ 

3(CnH2n+]-OH)+Cl3P. 

A  consideration  of  the  possible  constitutional  formulae  for  sub- 
stances having  the  general  molecular  formula  CnH2n+2O  reveals  the 
fact  that  the  linkage  of  the  oxygen  atom  admits  of  only  two  possible 
formulae;  thus,  the  compound  C2H6O  could  be  either 

1.  CH3.CH2.OH,    or    II.  CH3.O.CH3. 

Since  all  the  hydrogen  atoms  in  the  second  formula  have  the 
same  value,  it  cannot  be  the  one  representing  an  alcohol,  as  it  would 
not  account  for  a  very  important  property  of  these  compounds, 
their  interaction  with  the  alkali-metals.  The  action  of  silver 
hydroxide  on  an  alkyl  iodide,  or  that  of  phosphorus  chlorides  on 
an  alcohol,  would  accord  equally  ill  with  this  formula,  whereas  for- 
mula I.  explains  these  reactions  fully.  It  must  therefore  be  adopted. 


40] 


ALCOHOLS,  CnH2n-f  i  -OH. 


51 


The  constitutional  formulae  of  the  alcohols  have  thus  been 
induced  from  their  properties.  Inversely,  the  constitutional  for- 
mulce  represent  all  the  chemical  properties  of  the  compounds,  being 
simply  a  short  way  of  expressing  them.  The  value  of  these  for- 
mulae is  evident:  the  structural  formula  of  a  compound,  estab- 
lished by  the  study  of  some  of  its  properties,  reveals  the  rest  of 
these  properties.  The  existence  of  properties  thus  deduced  has 
in  many  instances  been  established  by  experiment. 

Nomenclature  and  Isomerism. 

40.  The  alcohols  of  this  series  are  named  after  the  alkyl-groups 
contained  in  them;  for  example,  methyl  alcohol,  ethyl  alcohol,  propyl 
alcohol,  etc. 

Isomerism  may  arise  in  three  ways:  by  branching  of  the  carbon 
chains;  by  changing  the  position  of  the  hydroxyl-group;  or 
through  both  these  causes  simultaneously. 

This  is  seen  from  the  following  table  of  the  isomeric  alcohols 
C3  to  Cfi. 


Name. 

Formula. 

Melting- 
point. 

'  Boiling- 
point. 

Specific 
Gravity 
at  20° 

(d**-.) 

Propyl  alcohols  C3H8O 
1.  Normal 

2.  iso 
Butyl  alcohols  C4H10O 
1.  Normal  primary 
2.        ,  ,       secondary 

3.  iso 
4.  Trimethylcarbinol 
Amyl  alcohols  C5Hi2O 
1.  Normal  primary 
2.  isoButylcarbinol 
3.  Secondary   butyl- 
carbinol 
4.  Methylpropylcar- 
binol 
5.  Methylisopropyl- 
carbinol 
6.  Diethylcarbinol 
7.  Dimethylethylcar- 
binol 
8.  Tertiary  butylcar- 
binol 

CH3-CH2-CH2OH 
CH3-CHOH-CH3 

CH3-CH2-CH2-CH2OH 
CH3-CH2-CHOH-CH3 

(CH3)2CH-CH2OH 
(CH3)3C-OH 

CHS-(CH2)3-CH2OH 
(CH3)2CH-CH2-CH2OH 

CH3-CH(C2H5)-CH2OH 
CH3-(CH2)2-CHOH-CH3 

(CH3)2CH-CHOH-CH3 
C2H5-CHOH-C2H5 

(CH3)2C(OH)-C2H5 
(CH3)3CvCH2OH 

Glass- 
like 

-85-8° 

-79-6° 
Glass- 
like 
do. 
25-5° 

-134° 

97° 

81° 

117° 
100° 

107° 

83° 

138° 
131° 

128° 
119° 

112-5° 
117° 

102° 
112° 

0-804 
0-789 
0-810 

0-806 
0-786 

0-815 
0-810 







52 


ORGANIC  CHEMISTRY. 


[§  41 


The  alcohols  with  names  ending  in  "carbinol"  are  so  called 
because  all  alcohols  may  be  looked  upon  as  methyl  alcohol  (car- 
binol),  in  which  one  or  more  of  the  hydrogen  atoms,  with  the 
exception  of  the  one  in  the  hydroxyl-group,  are  replaced  by  alkyl- 
groups  (KOLBE).  Thus,  zsobutyl  alcohol  is  called  isopropylcarbinol, 
secondary  butyl  alcohol  methylethylcarbinol,  normal  butyl  alcohol 
n-propylcarbinol,  and  so  on. 

The  table  also  shows  that  in  a  primary  alcohol  the  hydroxyl- 
group  is  linked  to  a  primary  carbon  atom  (36),  and  that  in  a  second- 
ary or  a  tertiary  alcohol  the  hydroxyl  is  linked  to  a  secondary 
or  a  tertiary  carbon  atom  respectively.  Similarly,  any  compounds 
which  may  be  regarded  as  produced  by  replacement  of  hydrogen 
linked  to  a  primary,  secondary,  or  tertiary  atom  are  called  primary, 
secondary,  or  tertiary  compounds.  Primary  alcohols  are  repre- 
sented by  the  general  formula  CnH2n+1 — CH2OH;  secondary  by 

/H 

CTT  r\/     p      TT 

n£12n-fl       ^^— ^mrL2m+l> 
\OH 

and  tertiary  by 


41, 


General  Properties  of  the  Alcohols. 

Some  of  the  physical  properties  of  the  alcohols  are  given 


in  this  table,  which  includes  only  normal  primary  compounds. 


Name. 

Formula. 

Melting- 
point. 

Boiling- 
point. 

Difference  of 
the  Boiling- 
points. 

Specific 
Gravity. 

Methyl  alcohol 

CH3OH 

-  97-1° 

67-4° 

0-812 

Ethyl           » 

C?H5OH 

-114-15° 

78° 

13-3° 

0-806 

Propyl 

CSH7OH 



96-5° 

18-5° 

0-817 

Butyl 

C4I19OH 

-  79-6° 

116-7° 

20-2° 

0-823 

Aniyl 

C^aHnO-H. 

— 

137° 

20-3° 

0-829 

Hexyl 

CCH13OH 



157° 

20° 

0-833 

Heptyl 

C7H15OH 

-  36-5° 

175° 

18° 

0-836 

Octyl 

CsHnOH 

-   17-9° 

194-5° 

19-5° 

0-839 

Nonyl          » 

C9Hi9OH 



213° 

18-5° 

0-842 

This  table,  with  that  in  40,  shows  that  the  normal  compounds 
have  the  highest  boiling-points  (38). 


§•42]  METHYL  ALCOHOL.  53 

The  augmentation  of  the  molecule  by  addition  of  the  CH2- 
group  is  attended  by  an  almost  constant  rise  in  boiling-point, 
although  for  the  first  members  the  rise  is  somewhat  less  than 
for  the  alcohols  higher  in  the  series.  The  association  of  the 
alcohol  molecules  renders  SYDNEY  YOUNG'S  formula  inapplica- 
ble (33). 

The  existence  of  this  association  is  proved  in  three  ways:  (1) 
The  vapour-densities  of  the  alcohols  at  temperatures  slightly  above 
their  boiling-points  are  greater  than  indicated  by  their  formulae; 
(2)  the  degree  of  association  can  be  inferred  from  measurements 
of  the  capillarity  and  viscosity  of  the  liquids;  (3)  there  subsists 
between  the  boiling-point  and  the  molecular  weight  a  relationship 
of  the  type 


T  being  the  absolute  boiling-point,  and  M  the  molecular  weight. 
For  many  compounds  the  constant  has  the  value  64,  but  it  is  much 
greater  for  associated  substances,  and  increases  with  the  degree  of 
association.  This  formula  also  affords  a  means  of  detecting  asso- 
ciation. 

The  lower  alcohols  (Ci  —  C4)  are  mobile  liquids,  the  middle 
members  (C5  —  Cn)  are  of  a  more  oily  nature,  while  the  higher 
members  are  solid  at  the  ordinary  temperature.  In  thin  layers 
all  are  colourless.  In  thick  layers  they  are  slightly  yellow,  the 
colour  becoming  more  marked  with  increase  in  the  number  of 
carbon  atoms.  The  first  members  (Ci  —  €3)  are  miscible  in  all 
proportions  with  water,  but  the  solubility  of  the  higher  members 
diminishes  quickly  as  the  number  of  carbon  atoms  increases. 

The  lower  members  have  a  spirituous,  and  those  intermediate 
a  disagreeable,  smell;  while  the  solid  members  are  odourless. 
Their  specific  gravity  is  less  than  1. 

Methyl  Alcohol,  CH3'OH. 

42.  Methyl  alcohol  is  obtained  on  the  large  scale  by  the  dry 
distillation  of  wood  in  iron  retorts  at  as  low  a  temperature  as 
possible;  or  better,  by  treatment  of  wood  with  hot  producer-gas, 
which  is  a  mixture  of  carbon  monoxide  and  nitrogen,  obtained 
by  passing  air  over  coke  at  a  white  heat.  To  this  method  of 


54  ORGANIC  CHEMISTRY.  [§  43 

preparation  the  substance  owes  its  name  wood-spirit.  The 
products  of  the  distillation  are  gases,  an  aqueous  liquid,  and 
tar.  The  aqueous  solution  contains  1-2  per  cent,  of  methyl 
alcohol  and  a  number  of  other  substances,  the  chief  being  acetic 
acid  (82)  (ca.  10  per  cent.)  and  acetone  (in),  (ca.  0*5  per  cent.). 
The  acetic  acid  is  converted  into  calcium  acetate  by  the  action  of 
lime,  and  the  methyl  alcohol  purified  by  fractional  distillation, 
and  other  methods.  It  is  used  in  the  arts  in  the  preparation  of 
aniline-dyes  and  formaldehyde,  for  the  denaturation  of  spirit  to 
render  it  unfit  for  drinking  purposes  (44),  and  in  other  processes. 
Methyl  alcohol  burns  with  a  pale-blue  flame,  and  is  miscible 
with  water  in  all  proportions,  the  mixing  being  accompanied  by 
contraction  and  the  development  of  heat.  It  is  poisonous. 

Ethyl  Alcohol,  C2H5*  OH. 

43.  Ethyl  alcohol,  or  ordinary  alcohol,  is  prepared  artificially 
in  enormous  quantities.  Its  preparation  depends  upon  a  prop- 
erty possessed  by  dextrose  (208),  a  sugar  with  the  formula 
CeH12O6,  of  decomposing  into  carbon  dioxide  and  alcohol  in 
presence  of  yeast-cells: 

C6H12O6  =  2C2H6O  +  2CO2. 

About  95  per  cent,  of  the  dextrose  decomposes  according  to  this 
equation.  By-products  such  as  glycerol  and  other  substances 
are  also  formed.  Certain  higher  alcohols  of  this  series,  princi- 
pally amyl  alcohols,  and  also  a  small  proportion  of  succinic  acid, 
are  produced  from  the  proteins  contained  in  the  raw  material 

(242)- 

On  account  of  its  cost,  dextrose  itself  is  not  employed  in  the 
manufacture  of  alcohol,  some  substance  rich  in  starch  (225), 
(C6Hi0O5)n,  such  as  potatoes,  grain,  etc.,  being  used  instead. 
By  the  action  of  enzymes  (222),  the  starch  is  almost  completely 
transformed  into  maltose  (214),  Ci2H22On,  one  molecule  of  this 
compound  being  then  converted  into  two  molecules  of  dextrose 
by  the  action  of  one  molecule  of  water: 


i2H22On  +  H2O  = 

Maltose  Dextrose 


43] 


ETHYL  ALCOHOL. 


55 


The  enzyme  employed  in  the  technical  manufacture  of  maltose 
from  starch  is  called  diastase,  and  is  present  in  malt.  The  reaction 
it  induces  is  called  sac- 
charification.  When  po- 
tatoes are  used,  they  are 
first  made  into  a  thin, 
homogeneous  pulp  by 
treatment  with  steam 
under  pressure  at  140°  to 
150°,  malt  being  added 
after  cooling.  At  a  tem- 
perature of  60°  to  62°, 
the  decomposition  into 
maltose  is  completed  in 
twenty  minutes. 

Yeast  is  then  added 
to  the  maltose  solution, 
and  the  fermentation  car- 
ried on  between  23°  and 
25°.  To  separate  the  re- 
sulting alcohol  from  the 
other  substances  present, 

the  product  is  submitted  to  distillation;  and  by  using  a  fraction- 
ating-column  (Fig.  23),  alcohol  of  90  per  cent,  strength  can  be 
obtained,  although  the  concentration  of  the  alcohol  in  the 
fermented  liquid  does  not  exceed  18  per  cent. 

The  thin  liquid  residue  remaining  in  the  still  is  called  spent 
wash,  and  is  used  for  feeding  cattle,  it  contains,  amongst  other 
products,  almost  all  the  proteins  present  in  the  material  from  which 
the  spirit  has  been  manufactured. 

The  crude  spirit  (low  wines)  so  prepared  is  again  carefully 
fractionated,  when  alcohol  of  96  per  cent,  by  volume  (spirits)  is 
obtained.  The  fractions  of  higher  boiling-point  consist  of  an  oily 
liquid  of  unpleasant  odour,  called  fusel-oil:  it  contains  chiefly 
amyl  alcohols  and  other  homologues.  The  residue  is  called  spent 
lees. 

Alcoholic  beverages  are  classified  into  those  that  have  been  dis- 
tilled, and  those  that  have  not. 


FIG.  23. — FRACTIONATING-COLUMN. 


56 


ORGANIC  CHEMISTRY. 


[§44 


Distilled  (about  50  percent,  of  alcohol). 

Brandy  or  cognac,  from  wine. 

Whiskij,    from    fermented    solution 
of  malt. 

Rum,  from  fermented  solution  of 
sugar. 

Gin,    like     whisky,    but   flavoured 
with  juniper. 


Not  distilled. 


Beer,  from  fermented  malt  and  hops 
(3-6  per  cent,  of  alcohol). 

Winet  fermented  grape-juice  (8-10 
per  cent,  of  alcohol). 

"Fortified"  wines,  such  as  port, 
sherry,  and  madeira.  They  are 
wines  with  added  alcohol.  (Nat- 
ural wine  never  contains  more 
than  about  10  per  cent,  of  alcohol.) 


44.  The  alcohol  of  commerce  ("  spirits  of  wine  ")  always  con- 
tains water.  To  obtain  anhydrous  or  absolute  alcohol  from  this, 
lumps  of  quicklime  are  added  to  spirit  containing  a  high  per- 
centage of  alcohol,  until  the  quicklime  shows  itself  above  the 
surface  of  the  liquid.  The  latter  is  allowed  to  stand  for  some 
days,  or  boiled  for  several  hours  under  a  reflux-condenser  (17), 
and  then  distilled.  The  preparation  is  much  facilitated,  and 
the  loss,  rather  large  by  this  method,  reduced  to  a  minimum, 
by  heating  a  spirit  of  high  percentage  with  a  small  quantity  of 
quicklime  in  a  vat,  closed  by  a  screwed-down  cover,  for  some 
hours  at  100°  in  a  water-bath.  The  spirit  is  then  distilled.  To 
prepare  absolute  alcohol  from  dilute  alcohol,  the  latter  must  first 
be  concentrated  by  distillation  from  a  water-bath.  The  de- 
hydration can  also  be  effected  by  addition  of  solid  potassium 
carbonate,  which  causes  the  liquid  to  separate  into  two  layers, 
the  aqueous  one  below  and  the  alcoholic  one  above.  Alcohol  of 
91*5  per  cent,  by  weight  is  thus  obtained. 

Absolute  alcohol  is  a  mobile,  colourless  liquid  of  character- 
istic odour,  and  burns  with  a  pale-blue,  non-luminous  flame. 
Cooling  with  liquid  air  renders  it  very  viscid,  and  ultimately 
•causes  crystallization.  It  is  very  hygroscopic,  being  miscible  with 
water  in  all  proportions  with  contraction  and  rise  in  tempera- 
ture. The  maximum  contraction  is  obtained  by  mixing  52 
volumes  of  alcohol  with  48  volumes  of  water,  the  volume  of  the 
resulting  mixture  at  20°  being  96*3  instead  of  100. 

The  presence  of  water  in  alccrhol  can  be  detected  by  anhydrous 
•copper  sulphate,  which  remains  p3rfectly  colourless  when  in  con- 
tact with  absolute  alcohol,  whereas  if  a  trace  of  water  is  present, 


§44]  .    ETHYL  ALCOHOL.  57 

the  copper  sulphate  develops  a  light-blue  colour  after  several  hours. 
The  specific  gravity,  a  physical  constant  often  employed  to 
ascertain  the  purity  of  liquid  compounds,  can  also  be  employed 
for  the  same  purpose.  A  method  of  detecting  and  estimating 
very  slight  traces  of  water  in  alcohol  is  described  in  67. 

A  simple  and  rapid  method  for  the  estimation  of  alcohol  in 
mixtures  with  water  is  very  necessary  for  industrial  and  fiscal 
purposes,  and  a  practical  method,  due  to  VON  BAUMHAUER, 
MENDELEEFF,  and  others,  consists  in  the  determination  of  the 
specific  gravity  and  temperature  of  such  a  mixture.  A  table  has 
been  prepared  with  great  accuracy,  showing  the  specific  gravities 
of  mixtures  of  alcohol  and  water  from  0  to  100  per  cent.,  at 
temperatures  between  0°  and  30°.  When  the  specific  gravity 
and  temperature  of  a  given  mixture  have  been  determined,  the 
percentage  of  alcohol  may  be  found  by  reference  to  the  table.  In 
practice  the  specific  gravity  is  usually  determined  with  a  delicate 
hydrometer. 

In  commerce  and  in  the  arts,  the  amount  of  alcohol  is  usually 
expressed  on  the  Continent  of  Europe  in  volume-percentage,  or  the 
number  of  litres  of  absolute  alcohol  contained  in  100  litres  of  the 
aqueous  solution.  In  Great  Britain  the  standard  is  proof-spirit. 
This  name  is  derived  from  the  old  method  of  testing  spirit  by  moisten- 
ing gunpowder  with  it,  and  then  bringing  the  mixture  into  contact 
with  a  lighted  match.  If  the  alcohol  were  "under  proof,"  the 
powder  did  not  take  fire,  but  if  there  were  sufficient  alcohol  present, 
the  application  of  the  light  ignited  the  gunpowder,  the  spirit  being 
then  "over  proof."  When  the  proportions  of  alcohol  and  water 
were  such  that  it  was  just  possible  to  set  fire  to  the  powder,  the 
sample  was  described  as  "proof-spirit."  When  the  spirit  is  weaker 
than  proof-spirit  it  is  said  to  be  under  proof,  and  when  stronger 
than  proof-spirit  is  said  to  be  over  proof;  for  example,  a  spirit  5° 
under  proof  would  contain  in  each  100  volumes  the  same  quantity 
of  alcohol  as  95  volumes  of  proof-spirit,  and  a  spirit  5°  over  proof 
would  need  5  volumes  of  water  added  to  each  100  volumes  to  con- 
vert it  into  proof -spirit.  By  Act  of  Parliament  "proof-spirit"  is 
defined  as  "such  a  spirit  as  shall  at  a  temperature  of  51°  F.  weigh 
exactly  ff  of  an  equal  measure  of  distilled  water,"  corresponding 
with  a  spirit  containing  57.1  per  cent,  of  alcohol  by  volume,  or 
49.3  per  cent  by  weight. 

For  scientific  purposes  the  amount  of  alcohol  is  usually  ex- 
pressed in  percentage  by  weight,  or  the  number  of  grammes  of 


58  ORGANIC  CHEMISTRY.  [§  41 

alcohol  contained  in  100  grammes  of  the  aqueous  solution.  These 
percentage-numbers  are  not  the  same,  the  percentages  by  weight 
being  smaller  than  those  by  volume  for  a  spirit  of  any  given  con- 
centration. 

The  greater  part  of  the  alcohol  produced  is  consumed  in  the 
Form  of  beverages,  their  detrimental  physiological  effects  being 
augmented  by  the  impurities,  especially  fusel-oil,  which  they 
contain.  Alcohol  is  used  in  commerce  for  the  preparation  of 
lacquers,  varnishes,  dyes,  important  pharmaceutical  preparations 
such  as  chloroform,  chloral,  iodoform,  and  others,  and  as  a  motive 
power  for  motor-vehicles.  It  is  also  employed  for  the  preserva- 
tion of  anatomical  specimens.  Alcohol  is  a  good  solvent  for 
many  organic  compounds,  and  finds  wide  application  in  laboratory- 
work  for  this  purpose. 

On  account  of  the  extensive  use  of  alcohol  for  manufacturing 
processes,  some  industries  would  be  paralyzed  if  the  necessary 
spirit  were  subject  to  the  same  excise-duty  as  alcohol  intended 
for  consumption.  The  alcohol  used  in  manufactures  in  some 
countries  is  accordingly  made  unfit  for  drinking  (denatured  or 
methylated)  by  the  addition  of  materials  which  impart  to  it  a 
nauseous  taste,  and  is  sold  duty-free.  On  the  Continent  of  Europe 
crude  wood-spirit  is  employed  for  this  purpose,  and  in  Great 
Britain  this  is  supplemented  by  the  addition  of  a  small  quantity 
of  paraffin-oil.  The  sale  of  denatured  alcohol  is  also  permitted 
in  the  United  States. 

In  the  United  States  the  tax  on  alcohol  is  $1.10  per  proof  gallon 
(50  per  cent,  alcohol  by  volume),  or  $2.07  per  standard  gallon 
(231  cubic  inches  of  94  per  cent,  alcohol  by  volume).  The  duty  is 
much  higher  in  Great  Britain,  being  14s.  9d.  per  gallon  of  proof-spirit 
(British  standard,  p.  57).  Besides  permitting  the  sale  of  methyl- 
ated spirit  containing  naphtha,  the  British  Government  allows 
the  sale  for  manufacturers'  use  of  alcohol  denatured  with  wood- 
spirit  only,  under  the  name  "Industrial  spirit."  It  has  the  import- 
ant advantage  of  being  wholly  miscible  with  water.  In  the  chemical 
laboratories  of  universities  and  colleges  in  Great  Britain  and 
Ireland,  the  use  of  duty-free  pure  alcohol  is  permitted. 

A  test  for  ethyl  alcohol  is  the  formation  of  iodoform  on  the 
addition  of  iodine  and  caustic  potash  (146). 


3  45]  PROPYL  ALCOHOL,  59 

/ 
Propyl  Alcohols,  C3H7.OH. 

45.  Two  propyl  alcohols  are  known,  one  boiling  at  97°  and 
having  a  specific  gravity  of  0-804,  the  other  boiling  at  81°  and 
having  a  specific  gravity  of  0-789.  In  accordance  with  the  prin- 
ciples which  have  been  stated,  only  two  isomerides  are  possible: 

CH3.CH2-CH2OH,    and    CH3-CH(OH)  -CH3. 

Normal  propyl  alcohol  uoPropyl  alcohol 

The  structure  to  be  assigned  to  the  substance  with  the  higher 
boiling-point,  and  that  to  the  substance  with  the  lower,  may  be 
determined  by  submitting  the  substances  to  oxidation.  From 
each  of  these  alcohols  is  thus  obtained  a  compound  with  the 
formula  C3HaO,  but  these  oxidation-products  are  not  identical. 
On  further  oxidation,  the  compound  C3H6O  (propionaldehyde), 
obtained  from  the  alcohol  of  higher  boiling-point,  yields  an  acid 
C3H602,  called  propionic  acid;  whereas  the  substance  C3H60 
(acetone),  formed  from  the  alcohol  of  lower  boiling-point,  is  con- 
verted into  carbon  dioxide  and  acetic  acid,  C2H402: 

C3H8O   (propyl  alcohol,  B.P.  97°)  -»  C3H6O   (propionaldehyde)  -> 
— *  C3H6O2  (propionic  acid) ; 

C3H8O  (rsopropyl  alcohol,  B.P.  81°)  — >  C3H6O  (acetone)  —> 
-»  CO2  +  C2H4O2  (acetic  acid). 

Propionic  acid  has  the  constitution  CH3-CH2-COOH,  and 
acetone  CH3-CO-CH3,  as  will  be  shown  later.  It  will  be  observed 
that  only  the  normal  alcohol  is  capable  of  forming  propionic 
acid,  because  the  production  of  this  substance  must  be  due  to  the 
replacement  of  two  hydrogen  atoms  by  one  oxygen  atom,  and 
with  the  normal  alcohol  this  can  only  yield  a  compound  with  the 
structure  assigned  to  propionic  acid.  On  the  other  hand,  the 
formation  of  a  substance  with  the  constitution  of  acetone  by  re- 
moval of  two  hydrogen  atoms  from  a  compound  C3HgO  is  only 
possible  when  the  latter  has  the  structure  of  ^sopropyl  alcohol. 
The  alcohol  of  higher  boiling-point  must  therefore  be  n-propyl 
alcohol,  and  that  boiling  at  the  lower  temperature  must  be  iso- 
propyl  alcohol. 

Oxidation  affords  a  general  me  hod  for  distinguishing  primary 
from  secondary  alcohols.  By  referring  to  the  formulae  given  in 


60  ORGANIC  CHEMISTRY.  [§  4f> 

40,  it  is  seen  that  all  primary  alcohols  contain  the  group  —  CH2OHr 
which  is  converted  by  oxidation  into  the  carboxyl-group  — C  ^  QTT, 

the  characteristic  group  of  organic  acids.     Further,  all  secondary 

I 

alcohols  contain  the  group  H*C'OH:  removal  of  the  two  hydro- 
gen atoms  from  this  yields  the  group  C:O,  characteristic  of  the 

i 

ketones  (no),  the  homologues  of  acetone.  The  oxidation  of  a  pri- 
mary alcohol  and  that  of  a  secondary  alcohol  produce  respectively 
an  acid  and  a  ketone  with  the  same  number  of  carbon  atoms  as  the 
original  alcohol. 

A  further  induction  may  be  made  from  these  reactions.  In 
the  conversion  of  normal  propyl  alcohol  into  propionic  acid,  as 
well  as  of  isopropyl  alcohol  into  acetone,  the  oxidation  occurs  at 
the  carbon  atom  already  linked  to  oxygen.  This  is  always  so, 
and  the  general  rule  may  be  stated  as  follows:  when  an  organic 
compound  is  submitted  to  oxidation,  the  molecule  is  attacked  at  the 
part  which  already  contains  oxygen — that  is,  where  oxidation  has 
already  begun. 

Normal  propyl  alcohol  is  obtained  by  fractionation  of  fusel- 
oil,  and  is  a  colourless  liquid  of  agreeable  odour.  It  is  miscible 
with  water  in  all  proportions.  isoPropyl  alcohol  is  also  a  liquid: 
it  is  not  present  in  fusel-oil,  but  can  be  obtained  by  the  reduction 
of  acetone  (in  and  150). 

Butyl  Alcohols,  C4H9-OH. 

46.  Four  butyl  akohols  are  known  (cf.  Table,  40),  which  is 
the  number  possible  according  to  the  theory,  and  it  is  necessary 
to  consider  whether  these  theoretically  possible  formula  are  in 
accord  with  the  properties  of  the  four  isomerides.  On  oxidation, 
the  two  alcohols  boiling  at  117°  and  107°  respectively  yield  acids 
with  the  same  number  of  carbon  atoms.  They  must  therefore 
have  the  structures  1  and  3  (Ibid.),  since  each  contains  the  group 
— CH2OH.  For  reasons  referred  to  later,  the  alcohol  boiling  at 
117°  is  considered  to  have  the  normal  structure  (1),  and  that  boil- 
ing at  107°  the  structure  (3).  A  third  butyl  alcohol,  boiling  at 
100°,  is  converted  by  oxidation  into  a  ketone  with  the  same  num- 
ber of  carbon  atoms,  showing  that  it  must  be  a  secondary  alcohol 
corresponding  with  structure  (2).  Lastly,  for  the  fourth,  which  is 


§  46]  BUTYL  ALCOHOLS.  61 

solid  at  ordinary  temperatures,  melting  at  25-5°  and  boiling  at 
83°,  since  three  of  the  theoretically  possible  structural  formulae 
have  been,  assigned  to  the  other  isomerides,  there  remains  only  the 
fourth  structure,  that  of  a  tertiary  alcohol.  This  structure  for  the 
alcohol  melting  at  25-5°,  thus  arrived  at  by  elimination,  is  in 
accordance  with  its  chemical  behaviour.  On  oxidation,  for  exam- 
ple, it  yields  neither  an  acid  nor  a  ketone  with  four  carbon  atoms, 
but  the  molecule  is  at  once  decomposed  into  substances  containing 
a  smaller  number  of  carbon  atoms.  Since  to  yield  on  oxidation 
an  acid  with  the  same  number  of  carbon  atoms,  an  alcohol  must 
contain  the  group  — CH2OH,  and  to  produce  a  ketone  with  the* 

same  number  of  carbon  atoms,  it  must  contain  the  group  H  •  C  •  OH, 

it  is  evident  that  neither  of  these  can  be  obtained  from  a  tertiary 
alcohol.  If  the  oxidation  takes  place  in  this,  as  in  every  other 
case,  at  the  carbon  atom  already  linked  to  oxygen,  it  must  result 
in  the  decomposition  of  the  molecule. 

The  foregoing  holds  for  tertiary  alcohols  in  general,  so  that 
oxidation  affords  a  means  of  distinguishing  between  primary, 
secondary,  and  tertiary  alcohols.  The  experimental  proof  can  be 
summed  up  as  follows. 

A  primary  alcohol  yields  on  oxidation  an  acid  with  the  same 
number  of  carbon  atoms:  a  secondary  alcohol  yields  on  oxidation  a 
ketone  with  the  same  number  of  carbon  atoms:  whereas  oxidation 
of  a  tertiary  alcohol  at  once  decomposes  the  molecule,  yielding  com- 
pounds with  a  smaller  number  of  carbon  atoms. 

Many  other  methods  of  ascertaining  whether  an  alcohol  is 
primary,  secondary,  or  tertiary  are  available,  one  of  the  simplest 
being  based  on  the  effects  of  heat.  Primary  alcohols  are  stable 
at  360°,  the  boiling-point  of  mercury.  At  this  temperature, 
secondary  alcohols  decompose,  yielding  chiefly  hydrocarbons  of 
the  series  CnH2n  (112)  and  water;  but  they  are  stable  at  218°, 
the  boiling-point  of  naphthalene.  At  the  last  temperature  tertiary 
alcohols  are  decomposed,  yielding  similar  products  to  those  formed 
from  secondary  alcohols  at  360°.  In  practice,  the  constitution  of 
any  alcohol  is  ascertainable  by  determining  its  vapour-density  at 
both  these  temperatures  with  VICTOR  MEYER'S  apparatus  (n), 
the  decision  being  based  on  the  normal  or  abnormal  character  of 
the  results  obtained. 


62  ORGANIC  CHEMISTRY.  [§  47 


Amyl  Alcohols,  C5HU.OH. 

47.  The  alcohols  containing  five  carbon  atoms  are  called  amyl 
alcohols.  There  are  eight  possible  isomerides,  and  all  are  known 
(cf.  Table,  40).  They  are  liquids  with  a  disagreeable  odour,  like 
that  of  fusel-oil.  isoButylcarbinol,  (CH3)2CH.CH2.CH2OH,  and 
secondary  butylcarbinol,  CH3»CH(C2H5)  -CH2OH,  are  the  prin- 
cipal constituents  of  fusel-oil  .(43)- 

Secondary  butylcarbinol  furnishes  a  very  remarkable  example 
of  isomerism.  It  is  shown  in  34  how  the  arrangement  of  the 
atoms  in  a  molecule  accounts  for  the  phenomenon  of  isomer- 
ism. A  careful  study  of  the  properties  of  a  compound  makes  it- 
possible  to  assign  to  it  a  structural  formula,  to  the  exclusion  of 
all  the  other  formulae  possible  for  its  known  molecular  composi- 
tion. On  the  other  hand,  any  given  structural  formula  represents 
only  one  compound,  since  such  a  formula  is  the  expression  of 
a  very  definite  set  of  properties:  when  they  are  unlike  for  two 
compounds,  the  difference  must  be  indicated  by  their  structural 
formula? . 

Nevertheless,  there  are  three  isomeric  amyl  alcohols  which  have 
been  shown  by  careful  examination  to  have  the  same  structural 

formula: 

CH3    p    H 
C2H5>    <CH2OH. 

That  they  have  this  constitution  is  proved  by  the  fact  that  on 
oxidation  they  yield  valeric  acid  with  the  structure 

CH3    p    H 
C2H5>    <COOH, 

as  can  easily  be  proved  by  synthesis  (164). 

The  three  amyl  alcohols  with  this  constitution  have  identical 
chemical  properties  and  nearly  all  their  physical  constants  are  the 
same.  One  of  the  latter,  however,  serves  to  distinguish  them  from 
one  another.  When  a  beam  of  plane-polarized  light  is  passed 
'through  layers  of  these  alcohols,  the  plane  of  polarization  is  rotated 
by  one  isomeride  to  the  left,  and  by  another  to  the  right,  while  the 
third  alcohol  produces  no  rotation.  The  first  two  are  said  to  be 
optically  active  (26,  2). 

Since  the  difference  between  optically  active  compounds  de- 
pends only  upon  a  physical  property,  while  their  chemical  proper- 


§  47]  AMYL   ALCOHOLS.  C3 

ties  are  identical,  it  may  be  asked  whether  this  difference  is  not  a 
purely  physical  one,  arising  from  differences  in  the  arrangement 
of  the  molecules,  such  as  is  supposed  to  exist  in  dimorphous  sub- 
stances. The  objection  to  this  view  is  twofold. 

First,  differences  in  the  arrangement  of  the  molecules  can  only 
be  supposed  to  exist  in  the  case  of  solid  substances,  because  it  is 
only  in  them  that  the  molecules  have  a  fixed  position  in  relation 
to  one  another.  It  is  assumed  that  the  molecules  of  liquids  and 
gases  are  free  to  move;  but  they,  too,  afford  examples  of  optical 
activity.  For  liquids  there  is  still  a  possibility  that  not  the  mole- 
cules themselves,  but  conglomerations  of  them  arranged  in  a  defi- 
nite manner  may  be  free  to  move.  Were  this  the  cause  of  optical 
activity,  on  conversion  into  gases  of  normal  vapour-density,  optic- 
ally active  liquids  should  produce  no  rotation  in  the  plane  of 
polarization.  That  they  actually  do  produce  this  rotation  was 
proved  by  BIOT,  and  later  by  GERNEZ.  This  phenomenon  cannot 
be  attributed  to  a  difference  in  the  arrangement  of  the  molecules, 
because  in  a  vapour  of  normal  density  each  molecule  is  capable 
of  independent  motion. 

Second,  the  optical  activity  is  displayed  in  derivatives  of  optic- 
ally active  substances. 

Hence  it  follows  that  an  explanation  of  the  rotation  of  the  plane 
of  polarization  by  liquids  and  dissolved  substances  must  be  sought  for 
in  the  internal  structure  of  the  molecules. 

It  is  now  necessary  to  determine  what  peculiarity  in  the  struc- 
ture of  the  molecules   causes  this  phenomenon.     The  following 
considerations  will  furnish  an  insight  into  this.    The  Icevo-rotatory 
amyl  alcoholt  with  the  constitution 
CH3     p     H 
C2H5>  ;<CH2OH, 

is  converted  by  the  action  of  gaseous  hydriodic  acid  into  amyl 
iodide,  with  the  structural  formula 
CH3     p     H 
C3H5;>  J<CR2l. 

This  compound  is  optically  active.  On  treatment  with  nascent 
hydrogen,  the  iodine  atom  is  replaced  by  hydrogen,  with  forma- 
tion of  pentanet 

CH3     p     H 
C2H5>    ^ 
This  compound  is  optically  inactive. 


64  ORGANIC  CHEMISTRY.  [§48 

If  amyl  iodide  is  subjected  to  the  action  of  ethyl  iodide  in  the 
presence  of  sodium,  there  results  a  heptane, 


and  this  substance  is  optically  active. 

An  examination  of  these  three  optically  active  substances  shows 
that  they  differ  from  optically  inactive  pentane  in  the  respect  that, 
of  the  four  groups  linked  to  the  central  carbon  atom,  in  the  latter 
two  (methyl)  are  similar,  whereas  in  the  others  they  are  all  dif- 
ferent. 

48.  VAN  'T  HOFF  has  shown  that  most  optically  active  compounds 
contain  at  least  one  carbon  atom  linked  to  jour  different  atoms  or 
groups;  and  he  has  designated  a  carbon  atom  so  linked  an  asymmetric 
carbon  atom. 

As  stated  above,  there  are  three  amyl  alcohols  with  the  same 
constitutional  formula,  of  which  one  is  dextro-rotatory,  the  second 
Isevo-rotatory,  and  the  third  optically  inactive.  Three  such  isom- 
erides  always  exist  when  there  is  one  asymmetric  carbon  atom  in 
the  molecule,  and  of  the  two  optically  active  substances  one  causes 
exactly  the  same  amount  of  dextro-rotation  as  the  other  of  laevo- 
rotation.  VAN  'T  HOFF  has  shown  that  the  existence  of  this  num- 
ber of  isomerides  is  a  necessary  consequence  of  the  presence  of 
one  asymmetric  carbon  atom  in  a  molecule,  provided  certain  as- 
sumptions are  made  regarding  the  relative  positions  of  the  atoms 
in  space.  These  assumptions  are  as  follows. 

The  quadrivalency  of  the  carbon  atom  has  its  origin  in  four 
points  of  attraction,  situated  on  its  outer  surface,  so  that  it  is 
able  to  link  itself  to  atoms  or  groups  of  atoms  in  four  directions. 
The  only  supposition  about  these  directions  in  agreement  with 
the  facts  is  that  the  carbon  atom  is  situated  at  the  centre  of  a  regular 
four-sided  figure  (tetrahedron)  with  its  Unkings  directed  toward  the 
angles  (Fig.  24).  By  putting  the  groups  R,  P,  and  Q  of  com- 
pounds CR2Q2,  CR2PQ,  or  CR3P  in  different  positions  in  two 
atom  models,*  it  is  always  possible  by  rotating  the  models  to 

*  The  comprehension  of  what  follows  will  be  considerably  facilitated  by 
the  construction  of  several  models  of  carbon  atoms  with  their  linkings.  This 
is  easily  done  by  cutting  out  a  sphere  from  a  cork  to  represent  the  carbon 
atom,  the  linkings  being  represented  by  moderately  thick  wires  about  ten 
centimetres  long,  with  ends  filed  to  a  point.  These  wires  are  fixed  in  the 


§  48]     VAN  'T   HOFF'S   THEORY  OF  STEREOISOMERISM. 


65 


FIG.  24. — CARBON 
TETRAHEDRON. 


bring  them  into  such  a  position  that  the  like  groups  coincide, 
showing  that  the  two  forms  are  identical.  Such  compounds  do 
not  exhibit  optical  isomerism. 

For  compounds  CMIPQS,  containing  four 
different  groups  and  therefore  an  asymmetric 
carbon  atom,  the  possibility  of  the  existence 
of  two  isomeric  forms  is  indicated.  It  is  seen 
from  Figs.  25  and  26  (and  still  better  from 
models)  that  for  these  four  groups  two  arrange- 
ments are  possible,  which  cannot  be  made  to 
coincide  in  any  position,  although  they  resemble  one  another  as 
an  object  resembles  its  reflection  in  a  mirror.  Such  a  figure  has 
no  plane  of  symmetry,  hence  the  name  "  asymmetric  carbon 
atom." 

It  is  thus  possible  to  understand  how  one  isomeride  causes 
as  much  dextro -rotation  as  the  other  laevo-rotation,  for  the 
arrangement  of  the  groups  relative  to  the  asymmetric  carbon  atom 
must  be  the  cause  of  the  rotation  of  the  plane  of  polarization.  If 
the  arrangement  of  the  groups  in  Fig.  25  produces  dextro-rotation, 


b 


\ 


'd         d< 


FIG.  25.  FIG.  26. 

ASYMMETRIC  C-ATOMS. 

then  the  inverse  arrangement  in  the  isomeride  in  Fig.  26  must  neces- 
sarily cause  an  equal  rotation,  but  in  an  opposite  direction. 

It  was  stated  above  that  not  merely  two,  but  three,  isomerides 
are  possible  when  there  is  one  asymmetric  carbon  atom  present  in 
the  molecule;  a  dextro-rotatory,  a  Isevo-rotatory,  and  an  optically 
inactive  isomeride.  It  has  been  proved  that  the  optically  inactive 
substance  is  composed  of  equal  parts  of  the  dextro-rotatory  and 
of  the  Isevo-rotatory  compound.  Since  these  rotations  are  equal 

cork  sphere  in  the  manner  shown  in  Fig.  24.  To  show  the  linking  of  the 
atoms  or  groups  of  atoms,  cork  spheres  of  diffe;e:it  colours  are  fastened  to 
the  ends  cf  the  wires,  the  different  colours  indicating  dissimilar  groups. 


66  ORGANIC  CHEMISTRY.  [§§  49,  50 

in  amount,  but  different  in  direction,  their  sum  has  no  effect  upon 
the  plane  of  polarization. 

This  isomerism  in  space,  called  stereochemical  isomerism  or  stereo- 
isomerism,  is  not  indicated  in  the  ordinary  structural  formulae 
written  in  one  plane:  hence  the  apparent  contradiction  that  a 
single  structural  formula  may  represent  two  different  compounds. 
VAN  'T  HOFF'S  theory,  however,  supports  the  fundamental  prin- 
ciple that  all  isomerism  has  its  origin  in  a  difference  in  the  arrange- 
ment of  the  atoms  in  the  molecule. 

In  addition  to  the  explanation  of  optical  isomerism  just  given, 
two  others  might  be  suggested,  although  both  can  be  shown  to  be 
untenable.  Thus,  the  four  linkings  of  the  carbon  atom  might  be 
supposed  unequal  in  value;  so  that  such  a  compound  as  CPaQ  could 
exist  in  isomeric  forms.  Experience  contradicts  this  assumption. 

This  phenomenon  might  also  be  supposed  to  be  due  to  a  differ- 
ence in  the  motion  of  the  atoms  in  the  molecule.  Then  isomerism 
could  no  longer  exist  at  absolute  zero,  since  atomic  motion  ceases 
at  this  point;  and  a  falling  temperature  should  cause  a  marked 
diminution  in  the  difference  between  the  optical  isomerides.  There 
is,  however,  not  the  slightest  indication  of  such  behaviour. 


Higher  Alcohols,  CnH2n+i-OH. 

49.  The  properties  of  the  higher  alcohols  are  mentioned  in  41. 
Here  may  be  cited  cetyl  alcohol,  C16H33-OH,  obtained  from  sper- 
maceti, and  myricyl  alcohol,  C30H61.OH,  obtained  from  wax.  The 
number  of  isomerides  of  these  higher  compounds  possible  is  very 
great,  while  the  number  actually  known  is  but  small.  Of  the 
higher  members  of  the  series,  only  the  normal  primary  compounds 
are  known. 


Alkoxides. 

50.  Alkoxides  (alcoholates)  are  compounds  obtained  from  alco- 
hols by  exchange  of  the  hydroxyl-hydrogen  atom  for  metals  (39). 
The  best  known  are  sodium  methoxide  (methylate),  CH3-ONa,  and 
sodium  ethoxide  (ethylate),  C2H5.ONa.  Both  are  white  powders, 
and  yield  crystalline  compounds  with  the  corresponding  alcohol. 


§  50]  ALKOXIDES.  67 

They  dissolve  readily  in  the  alcohols,  and,  as  will  be  seen  later,  are 
constantly  used  in  syntheses.  It  was  formerly  supposed  that  the 
addition  of  water  to  a  solution  of  an  alkoxide  converted  it  com- 
pletely into  an  alkali-metal  hydroxide,  and  liberated  an  equivalent 
quantity  of  alcohol;  but  LOBRY  DE  BRUYN  has  shown  this  to  be 
only  partly  true,  an  equilibrium  being  reached  in  the  reaction: 

C2H5ONa  +  H./)  <=*  C2H5OH  +  NaOH. 

A  proof  of  this  is  given  in  55.  It  follows  that  a  solution  of  sodium 
hydroxide  in  alcohol  is  partly  decomposed  into  water  and  sodium 
alkoxide. 

The  alcoholic  solution  of  sodium  ethoxide,  usually  obtained  by 
dissolving  pieces  of  sodium  in  absolute  ethyl  alcohol,  gradually 
becomes  brown  in  consequence  of  oxidation  to  aldehyde  (106). 
On  the  other  hand,  the  solution  of  sodium  methoxide  in  methyl 
alcohol  remains  unaltered,  and  therefore  is  employed  in  syntheses 
more  than  that  of  sodium  ethoxide. 

Only  the  alkali-metals  react  directly  with  alcohols  to  produce 
alkoxides.  Those  of  other  metals  can  be  prepared  by  the  inter- 
action of  solutions  in  liquid  ammonia  of  a  potassium  alkoxide  and 
a  salt,  an  example  being  the  precipitation  of  barium  ethoxide  by 
the  combination  of  potassium  ethoxide  and  barium  nitrate: 

2C2H5OK  +Ba(NO,),  =  (C2H50)2Ba  +2KN03. 

The  alkoxides  of  calcium,  strontium,  and  lead  have  been  prepared 
similarly. 


ALKYL  HALIDES,   ESTERS,   AND  ETHERS. 

51.  Many  compounds  containing  a  hydroxyl-group  are  known 
in  inorganic  chemistry:  they  are  called  bases,  and  display  a  close 
resemblance  in  properties.  This  similarity  may  be  attributed  to 
their  common  possession  of  the  group  OH,  which  is  present  in 
their  aqueous  solutions  as  an  ion. 

An  aqueous  solution  of  alcohol  does  not  conduct  an  electric 
current,  so  that  the  alcohol  is  not  ionized.  This  is  supported  by 
the  fact  that  such  a  solution  is  not  alkaline,  and  therefore  contains 
no  OH-ions. 

Notwithstanding  this  fact,  the  alcohols  possess  a  basic  charac- 
ter in  so  far  that,  like  bases,  they  combine  with  acids  with  elimi- 
nation of  water: 


M.[OH+H].R=M.R+HOH. 

Alcohol         Acid  Ester 

The  substances  formed  are  comparable  with  the  salts  of  inor- 
ganic chemistry,  and  are  called  compound  ethers  or  esters.  The  dif- 
ferent natures  of  bases  and  of  alcohols  are  displayed,  however,  in 
the  mode  of  formation  of  their  salts,  which  is  quite  unlike  that  in 
which  esters  are  produced.  A  salt  is  formed  from  an  acid  and 
base  instantaneously:  it  is  a  reaction  of  the  ions,  because  the 
hydrogen  ion  of  the  acid  unites  with  the  hydroxyl  ion  of  the  base 
•("  Inorganic  Chemistry,"  66): 

[B  +  OH']+[H+Z']  =  [B+Z']+H2O. 

Base  Acid  Salt 

'The  formation  of  esters,  on  the  other  hand,  takes  place  very  slowly, 
-especially  at  ordinary  temperatures,  the  reaction  being  between 
the  non-ionized  alcohol  and  the  acid: 

R.OH+[H+Z']  =  R.Z+H2O. 

Alcohol  Acid  Ester 

68 


§  52]  ALKYL  HAL1DES.  69 

Reactions  between  ions  usually  take  place  instantaneously, 
those  between  molecules  slowly. 

•  Many  bases  can  lose  water,  with  formation  of  anhydrides  or 
oxides:  alcohols  behave  similarly.  By  the  abstraction  of  one 
molecule  of  water  from  two  molecules  of  an  alcohol,  compounds 
called  ethers  with  the  general  formula  CnH2n+i  —  O  —  CnH2n+1  are 
formed.  By  elimination  of  water  from  two  different  alcohols,  com- 
pounds called  mixed  ethers  with  the  general  formula 

CnH2n-i-i  —  O  —  CmH2m+i 
are  produced. 

Alkyl  Halides. 

52.  The  alkyl  halides  may  be  regarded  as  the  hydrogen-halide 
esters  of  the  alcohols,  as  their  formation  from  alcohol  and  a  hydro- 
gen halide  shows: 

=  CnH2n+1 


In  preparing  alkyl  halides  by  this  method,  the  alcohol  is  first 
saturated  with  the  dry  hydrogen  halide,  and  then  heated  in  a 
sealed  tube  or  under  a  reflux-condenser.  The  reaction  may  also  be 
carried  out  by  heating  the  alcohol  with  sulphuric  acid  and  sodium 
or  potassium  halide: 

C2H5OH  +  H2SO4  +  KBr  =  C2H5Br  +  KHS04  +  H2O. 

Two  other  methods  of  formation  for  alkyl  halides  are  men- 
tioned in  28  and  39:  they  are  more  fully  treated  below. 

Action  of  Phosphorus  Halides  on  Alcohols.  —  These  sometimes 
react  together  very  energetically.  In  preparing  alkyl  bromides 
and  iodides,  it  is  usual  to  employ  phosphorus  with  bromine  or 
iodine  instead  of  the  bromide  or  iodide  of  phosphorus  itself.  For 
example,  in  the  preparation  of  ethyl  bromide,  red  phosphorus  is 
added  to  strong  alcohol,  in  which  it  is  insoluble.  Bromine  is  then 
added  drop  by  drop,  the  temperature  of  the  liquid  being  kept 
from  rising  by  a  cooling  agent.  Each  drop  of  bromine  unites  with 
phosphorus  to  form  phosphorus  tribromide,  and  it  reacts  with  the 
alcohol,  producing  ethyl  bromide: 

PBr3  +  3C2H5OH  =  P03H3  +  3C2H5Br. 

The  careful  addition  of  bromine  is  continued  until  a  quantity  cor- 
responding to  that  required  by  the  equation  has  been  used.     The 


70  ORGANIC  CHEMISTRY.  §53] 

mixture  is  then  allowed  to  stand  for  some  time,  so  that  the  reac- 
tion may  be  as  complete  as  possible,  the  final  product  consisting 
chiefly  of  phosphorous  acid  and  ethyl  bromide.  Since  the  latter 
boils  at  38-4°,  and  the  acid  is  not  volatile,  it  is  possible  to  separate 
them  by  distillation,  which  can  be  effected  by  immersing  the  flask 
containing  the  mixture  in  a  water-bath  heated  above  the  tempera- 
ture mentioned. 

Action  of  Halogens  on  Hydrocarbons.  —  Only  chlorides  and 
bromides  can  be  prepared  thus,  because  iodine  does  not  react  with 
hydrocarbons.  The  method  is  seldom  used  for  the  preparation  of 
alkyl  halides,  since,  from  two  causes,  mixtures  of  alkyl  halides  are 
obtained  which  are  sometimes  very  difficult  to  separate:  whereas, 
by  employing  other  methods,  these  compounds  are  produced  with- 
out admixture  of  similar  substances. 

One  of  these  causes  is  that  whenever  one  molecule  of  a  hydro- 
carbon CnH2n+2  is  brought  into  contact  with  one  molecule  of  chlo- 
rine or  bromine,  the  reaction  does  not  take  place  merely  as  indi- 
cated by  the  equation 


but  that  compounds  CnH2nCl2,  CnH2n_iCl3,  etc.,  are  simultaneously 
formed,  a  portion  of  the  hydrocarbon  remaining  unacted  on. 

SCHORLEMMER  observed  the  possibility  of  avoiding  the  formation 
of  these  higher  substitution-products  by  bringing  the  halogens  into 
contact  with  the  vapour  of  the  boiling  hydrocarbons. 

The  other  cause  is  that  the  halogen  replaces  hydrogen  in  dif- 
ferent positions  in  the  molecule.  Thus,  chlorine  reacts  with  nor- 
mal pentane  to  form  simultaneously  primary  and  secondary  amyl 
chlorides, 

CH3-CH2.CH2.CH2.CH2C1    and    CH3.CH2.CH2.CHC1.CH3, 

as  can  be  proved  by  converting  these  chlorides  into  the  corre- 
sponding alcohols  and  oxidizing  the  latter  (45). 

53.  The  following  table  gives  some  of  the  physical  properties 
of  the  alkyl  halides. 


§53] 


ALKYL   HALIDES. 


71 


d 

3 

Chloride. 

Bromide. 

Iodide. 

2 

">> 

Boiling- 
point 

Specific 
Gravity 

Boiling- 
point. 

Specific 
Gravity, 

Boiling- 
point. 

Specific 
Gravity. 

CH, 

Methyl 

-23-7° 

0-952(0°) 

4-5° 

1-732(0°) 

45° 

2-293(18°> 

C2H., 

Ethyl 

12-2° 

0-918(8°) 

38-4° 

1-468(13°; 

72-3° 

1-944(14°) 

C<H7 

ft-Propyl 

46-5° 

0-912(0° 

71° 

1-383(0°) 

102-5° 

1-786(0°) 

C4H8 

fi-Prim.  butyl 

78° 

0-G07(0°) 

101° 

1-305(0°) 

130° 

1-643(0°) 

C5HU 

Ai-Prim.  amyl 

107° 

0-901(0° 

129° 

1-246(0°) 

156° 

L543(0n) 

It  will  be  noticed  that  only  the  lower  chlorides  and  methyl 
bromide  are  gaseous  at  the  ordinary  temperature,  most  of  the 
others  being  liquids,  and  the  highest  members  solids.  The 
melting-points  of  some  of  these  compounds  have  been  determined 
accurately : 


Alkyl-Group. 

Name. 

Ch'oride. 

Bromide. 

Iodide.     » 

CH, 

C2H5 
C3H7 

Methyl 
Ethyl 
n-Propyl 

Below  -75° 
-119-0° 

-    66-1° 
-110-9° 
-101-4° 

-140.85° 

The  specific  gravities  of  all  the  chlorides  are  less  than  1,  and 
diminish  as  the  number  of  carbon  atoms  increases.  The  specific 
gravities  of  the  lower  bromides  and  iodides  are  considerably 
greater  than  1,  although  they  also  diminish  with  increase  in  the 
number  of  carbon  atoms,  so  that  the  highest  members  of  the 
homologous  series  are  specifically  lighter  than  water.  All  are 
very  slightly  soluble  in  water,  but  dissolve  readily  in  many  organic 
solvents.  The  lower  members  have  a  pleasant  ethereal  odour. 

Chemical  Properties. — In  their  action  upon  silver  nitrate  the 
alkyl  halides  differ  very  much  from  the  halides  of  the  metals.  In 
aqueous  or  alcoholic  solution  the  latter  at  once  yield  a  precipitate 
of  silver  halide,  the  reaction  being  quantitative.  On  the  other 
hand,  silver  nitrate  either  does  not  precipitate  silver  halide  from 
a  solution  of  the  alkyl  halides,  or  the  reaction  only  takes  place 
slowly.  The  explanation  is  the  same  as  that  given  in  51,  that  in 
the  first  case  the  action  is  one  between  ions,  and  in  the  second 
between  molecules.  This  proves  that  there  are  either  no  halogen. 


72  ORGANIC  CHEMISTRY.  [§54 

ions  present  in  an  alkyl  halide  solution,  or  at  least  that  their 
number  is  very  small. 

The  alkyl  halides  can  be  converted  into  one  another;  for 
example,  alkyl  iodides  can  be  obtained  by  heating  the  corre- 
sponding chlorides  with  potassium  or  calcium  iodide.  These 
reactions  are  often  incomplete. 

The  alkyl  iodides  are  chiefly  used  for  introducing  alkyl-groups 
into  organic  compounds: 

Alkyl  fluorides  are  also  known,  and  are  more  volatile  than  the 
corresponding  chlorides.  They  are  obtained  by  the  action  of  silver 
fluoride  on  an  alkyl  iodide,  and  in  other  ways. 

Esters  of  Other  Mineral  Acids. 

54.  Esters  of  a  great  number  of  mineral  acids  are  known.    The: 
general  methods  for  their  preparation  are  as  follows. 
1.  By  the  action  of  the  acid  on  absolute  alcohol: 


C2H5.[OH+H|.QN02  =  H2O  +  C2H5.ONO2. 

Alcohol  Nitric  acid  Ethyl  nitrate 

2.  By  the  action  of  an  alkyl  halide  on  a  silver  salt: 

S04[Ag2  +  21|C2H6  =  S04(C2H5)2+2AgI. 

Ethyl  sulphate 

3.  By  the  action  of  mineral-acid  chlorides  on  alcohols  or  alkox- 
ides: 

PO|Cl3  +  3Na|OC2H5  =  PO(OC2H5)3+3NaCl. 

Phosphorus  Normal  ethyl 

oxychloride  phosphate 

The  acid  esters  of  sulphuric  acid,  called  alkylsulphuric  acids, 
are  of  some  importance.  Ethylsulphuric  acid,  or  ethyl  hydrogen 
sulphate,  C2H5O-SO2»OH,  is  obtained  by  mixing  alcohol  with  con- 
centrated sulphuric  acid.  The  formation  of  this  compound  is  never 
quantitative,  because  an  equilibrium  is  reached  in  the  reaction 
(93)..  The  alkylsulphuric  acids  are  separated  from  the  excess  of 
sulphuric  acid  by  means  of  their  barium  (or  strontium  or  calcium) 
salts,  these  compounds  being  readily  soluble  in  water,  while  the 
sulphates  are  insoluble,  or  nearly  so.  It  is  only  necessary  to 
neutralize  the  mixture  of  sulphuric  acid  and  alkylsulphuric  acid 


:§  54]  ETHYLSULPHURIC  ACID.  73 

with  barium  carbonate,  the  product  being  a  solution  of  barium 

ba* 
•ethylsulphate,  ^  TT  >SO4.     The  free  ethylsulphuric  acid  is  then 

obtained  by  the  addition  of  the  calculated  quantity  of  sulphuric 
acid  to  this  solution.  At  ordinary  temperatures  it  is  an  odour- 
less, oily,  strongly  acid  liquid,  miscible  with  water  in  all  propor- 
tions. The  aqueous  solution  decomposes  into  sulphuric  acid  and 
alcohol,  slowly  at  the  ordinary  temperature,  but  quickly  at  the 
boiling-point. 

Ethylsulphuric  acid  forms  well-crystallized  salts.  Its  potas- 
sium salt  is  used  in  the  preparation  of  ethyl  compounds;  for  exam- 
ple, ethyl  bromide  is  readily  prepared  by  the  dry  distillation  of  a 
mixture  of  potassium  bromide  and  potassium  ethylsulphate: 


K  =  KO.S02.OK+C2H5Br. 

Potassium  ethyl-  Potassium  Ethyl 

sulphate  sulphate  bromide 

When  free  ethylsulphuric  acid  is  heated,  the  neutral  ethyl  ester 
of  sulphuric  acid  and  free  sulphuric  acid  are  formed : 

SO2  <  f^TJ  +  SO2  <  f~\n     TT        =     SO2  <  y-XTT  +  SO2  <  f^f^     TT     . 

VyXl  v/V_^2JLlg  vy£l  wV^O-tj-S 

Simultaneously,  free  sulphuric  acid  and  ethylene  are  produced 


The    conversion    of    ethylsulphuric    acid    into   ether   is  described 
in  56. 

Dimethyl  sulphate,  (CH3)2S04,  is    obtained  by  the  vacuum-dis- 
tillation of  methylsulphuric  acid: 

2CH3HS04  =  (CH3)2S04  +H2S04. 

It  is  an  oily  liquid,  boiling  at  188°,  and  is  often  employed  in  the 
introduction  of  methyl-groups  into  organic  compounds. 


74  ORGANIC    CHEMISTRY.  [§§55,56 


Ethers. 

55.  The  ethers  are   isomeric  with  the  alcohols.      Their  con« 
stitution  is  proved  by  WILLIAMSON'S  synthesis,  the  action  of  an 
alkoxide  on  an  alky  I  halide: 

CnH2n+1.O.CmH2m+1+NaI. 

This  synthesis  affords  confirmation  of  the  constitution  of  the 
alkoxides  indicated  in  39,  that  the  metal  occupies  the  place  of 
the  hydroxyl-hydrogen.  For,  supposing  it  were  otherwise,  the 
metal  having  replaced  a  hydrogen  atom  directly  linked  to  carbon, 
then  sodium  methoxide,  for  example,  would  have  the  formula 
Na-CH2-OH.  On  treatment  with  ethyl  iodide,  this  compound 
would  yield  propyl  alcohol: 

C2H5.[TTNa1-CH2OH  =  C2H5 .  CH2OH  +  Nal. 

This  reaction  does  not  take  place.  Methylethyl  ether,  with  the 
empirical  formula  of  an  alcohol,  but  none  of  its  properties,  is  pro- 
duced instead. 

WILLIAMSON'S  synthesis  is  also  possible  when  the  alkoxide  is  dis- 
solved in  dilute  alcohol  (50  per  cent.).  Though  so  much  water  is 
present,  the  reaction  is  almost  quantitative.  It  follows  that  the 
greater  part  of  the  sodium  alkoxide  must  be  present  as  such,  and 
is  therefore  not  decomposed  by  the  water  into  alcohol  and  sodium 
hydroxide  (50),  because  then  the  formation  of  the  ether  would  neces- 
sarily be  prevented. 

56.  The  best-known   compound   of  the  homologous  series  of 
ethers    is   diethyl   ether,    C2H5.O.C2H5,    usually    called    "ether." 
This  compound  is  manufactured,  and  also  prepared  in  the  labora- 
tory, from  sulphuric  acid  and  ethyl  alcohol.     For  this  purpose  a 
mixture  of  five  parts  of  alcohol  (90  per  cent.)  is  heated  with  nine 
parts  of  concentrated  sulphuric  acid  at  130°- 140°.     When  ether 
and  water  begin  to  distil,  alcohol  is  allowed  to  flow  into  the  dis- 
tillation-flask to  keep  the  volume  of  liquid  constant.     Ether  passes 
over  continuously,  but  after  about  six  times  as  much  alcohol  has 
been  added  as  was  in  the  first  instance  mixed  with  the  sulphuric 
acid,  the  distillate  becomes  richer  and  richer  in  alcohol,  and  finally 


§56]  ETHER.  75 

the  formation  of  ether  stops  altogether.  Methylated  spirit  may  be 
substituted  for  pure  spirit,  the  product  being  called  "methylated 
ether." 

The  explanation  of  this  process  is  as  follows.  The  alcohol  and 
sulphuric  acid  first  form  ethylsulphuric  acid  (54).  Ethylsulphuric 
acid  is  decomposed  by  heating  with  water,  the  acid  and  alcohol 
being  regenerated: 


C2H5.|QSO3H+H]OH  =  C2H5.OH+H2S04. 

When,  however,  ethyl  alcohol  instead  of  water  reacts  with  ethyl- 
sulphuric  acid,  ether  and  sulphuric  acid  are  formed  in  an  exactly 
analogous  manner: 

C2H5 .  |  O  •  SO3HTHl  •  O  -  C2H5  =  C2H5.O.C2H5+H2S04. 

The  production  of  ether  depends  upon  the  formation  of  ethyl- 
sulphuric  acid,  and  subsequent  decomposition  of  this  compound 
into  ethyl  ether  and  sulphuric  acid  by  the  addition  of  more  alcohol. 
Since  the  sulphuric  acid  is  regenerated  in  this  reaction,  it  yields 
a  fresh  quantity  of  ethylsulphuric  acid,  so  that  the  process  is  con- 
tinuous. This  would  lead  to  the  expectation  that  a  small  quan- 
tity of  sulphuric  acid  could  convert  an  unlimited  amount  of  alco- 
hol into  ether,  but  this  is  not  borne  out  by  experience.  The 
explanation  is  that  in  the  formation  of  ethylsulphuric  acid  from 
alcohol  and  sulphuric  acid,  water  is  formed  as  a  by-product: 

C2H5.[OHTHlS04H  =  C2H5-S04H+H20. 

This  water  partly  distils  along  with  the  ether,  but  partly  remains 
in  the  flask,  decomposing  the  ethylsulphuric  acid  as  formed  into 
alcohol  and  sulphuric  acid.  When  the  amount  of  water  in  the 
reaction-mixture  exceeds  a  certain  limit,  it  prevents  the  formation 
of  ethylsulphuric  acid  altogether,  thus  putting  an  end  to  the  pro- 
duction of  ether. 

When  another  alcohol  is  allowed  to  flow  into  the  original  mix- 
ture instead  of  ethyl  alcohol,  shortly  before  the  distillation  begins, 
a  mixed  ether  is  obtained : 


C2H5.[S04HjJ^.O.C5H11 


76  ORGANIC  CHEMISTRY.  [§56 

This  reaction  proves  that  the  formation  of  ether  takes  place  in 
the  two  stages  mentioned  above. 

SENDERENS  found  that  addition  to  the  liquid  of  five  per  cent, 
of  its  weight  of  sulphate  of  aluminium  or  lead  causes  the  forma- 
tion of  ether  smoothly  at  120°. 

Higher  homologues  of  ethyl  ether  cannot  be  prepared  by  heat- 
ing the  higher  alcohols  with  sulphuric  acid,  even  in  presence  of  the 
sulphates  named,  only  unsaturated  hydrocarbons  of  the  series 
CnH2n  being  produced.  Ethyl  ether  is  also  formed  by  passing 
. alcohol- vapour  over  aluminium  oxide  at  240°-260°. 

The  crude  ether  thus  obtained  contains  water,  alcohol,  and  small 
quantities  of  sulphur  dioxide.  It  is  left  in  contact  with  quicklime 
for  several  days,  the  water,  sulphur  dioxide,  and  part  of  the  alcohol 
being  thus  removed.  It  is  then  distilled  from  a  water-bath  heated 
to  about  55°.  To  remove  the  small  quantity  of  alcohol  remaining, 
it  is  extracted  several  times  with  small  volumes  of  water,  and  the 
water  run  off.  The  ether  is  separated  from  dissolved  water  by  dis- 
tillation, first  over  calcium  chloride  and  finally  over  sodium. 

Diethyl  ether  is  a  colourless,  very  mobile  liquid  of  agreeable 
-odour,  boiling  at  35-4°,  and  solidifying  at  -117'6°.  Pro- 
longed breathing  of  it  produces  unconsciousness,  followed  by  but 
slightly  disagreeable  consequences  on  awakening.  Ether  is  there- 
fore used  in  surgery  as  an  anaesthetic.  It  is  slightly  soluble  in 
water,  one  volume  dissolving  in  11  •!  volumes  of  water  at  25°; 
water  also  dissolves  slightly  in  ether  (2  per  cent,  by  volume 
at  12°).  On  account  of  its  low  boiling-point,  ether  is  very 
volatile,  and  as  its  vapour  is  highly  combustible,  burning  with  a 
luminous  flame,  and  producing  an  explosive  mixture  with  air,  it 
is  a  substance  requiring  very  careful  handling.  Intense  cold  is 
produced  by  its  evaporation,  the  outside  of  a  flask  containing  it 
becoming  coated  with  ice  when  the  evaporation  of  the  ether  is 
promoted  by  the  introduction  of  a  rapid  stream  of  air. 

In  the  laboratory,  ether  is  an  invaluable  solvent  and  crystal- 
lizing-medium  for  many  compounds,  and  is  used  for  extracting 
aqueous  solutions  (23).  It  is  also  of  great  utility  in  many  manu- 
facturing processes. 


ALKYL-RADICALS  LINKED  TO  SULPHUR. 

57.  The  elements  grouped  in  the  same  column  of  the  periodic 
system  ("Inorganic  Chemistry/'2i3-22i)  yield  similar  compounds, 
a  fact  traceable  to  their  having  equal  valencies:  they  also  have 
similar  chemical  properties.  Experience  has  shown  that  organic 
compounds  containing  elements  of  such  a  group  display  the  proper- 
ties of  their  inorganic  analogues  in  every  variety  of  similarity  and 
dissimilarity,  their  points  of  resemblance  and  of  difference  being 
sometimes  even  more  marked  than  those  of  the  inorganic  com- 
pounds. A  comparison  of  the  oxygen  compounds  treated  of  up  to 
this  point  with  the  sulphur  compounds  of  similar  structure  will 
serve  as  an  example. 

The  alcohols  and  ethers  may  be  regarded  as  derived  from  water 
by  the  replacement  of  one  or  both  of  its  hydrogen  atoms  by  alkyl. 
The  corresponding  sulphur  compounds  are  similarly  derived  from 
sulphuretted  hydrogen,  and  are  represented  thus: 

H    and 

The  first  are  called  mercaptans,  and  the  second  thioethers. 

The  resemblance  of  these  compounds  to  the  alcohols  and  ethers 
is  chiefly  noticeable  in  their  methods  of  formation,  for  if  potas- 
sium hydrogen  sulphide  instead  of  potassium  hydroxide  reacts 
with  an  alkyl  halide,  a  mere  apt  an  is  formed: 

CnH2n+1.[X+Kl-SH  =  CnH2n+l.SH+KX. 


Like  the  alcohols,  the  mercaptans  have  one,  and  only  one, 
hydrogen  atom  in  the  molecule  replaceable  by  metals.  It  is  there- 
fore reasonable  to  suppose  that  the  hydrogen  atom  thus  distin- 
guished from  all  the  others  is  linked  to  sulphur,  the  other  hydrogen 
atoms  being  linked  to  carbon. 

77 


78  ORGANIC   CHEMISTRY.  [§  5g 

Just  as  the  ethers  are  formed  by  the  action  of  alkyl  halides  on 
alkoxides,  so  the  thioethers  are  obtained  by  treating  the  metallic 
compounds  of  the  mercaptans,  the  mercaptides,  with  alkyl  halides: 


H2n+1.S.[NiTPl|.CmH2m+1  =  CnH2n+1.S.CmH2m+1+NaI. 


Water  is  a  neutral  compound,  and  sulphuretted  hydrogen  is  a 
weak  acid;  in  consequence  alcohol  does  not  form  alkoxides  with 
the  bases  of  the  heavy  metals,  whereas  mercaptans  yield  mercap- 
tides with  them.  An  alcohol  soluble  with  difficulty  in  water,  such 
as  amyl  alcohol,  does  not  dissolve  in  alkalis;  but  the  mercaptans, 
although  insoluble  in  water,  dissolve  readily  in  alkalis,  forming 
mercaptides.  They  therefore  possess  an  acidic  character. 

Mercaptans. 

58.  The  mercaptans  can  also  be  obtained  by  the  action  of  phos- 
phorus pentasulphide  upon  alcohols : 

5CnH2n+1.OH  +  P2S5  -*5CnH2n+1.SH; 

or  by  distilling  a  solution  of  potassium  alkylsulphate  with  potas- 
sium hydrogen  sulphide: 

~~]SH  =  C2H5.SH  +  K 


They  are  liquids  almost  insoluble  in  water,  with  boiling-points 
markedly  lower  than  those  of  the  corresponding  alcohols.  Thus, 
methyl  mercaptan  boils  at  6°,  methyl  alcohol  at  66°,  a  striking 
phenomenon,  sulphur  being  much  less  volatile  than  oxygen.  It 
may  be  explained  by  assuming  non-association  of  the  mercaptan 
molecules,  and  association  of  the  alcohol  molecules.  The  mercap- 
tans are  characterized  by  their  exceedingly  disagreeable  odour,  a 
property  characteristic  of  almost  all  volatile  sulphur  compounds. 
Our  olfactory  organs  are  very  sensitive  to  mercaptans,  and  can 
detect  the  merest  traces  of  them,  although  quite  unrecognizable 
by  chemical  means.  The  smell  of  the  perfectly  pure  mercaptans 
is  much  less  objectionable  than  that  of  the  crude  products. 

Many  metallic  compounds  of  the  mercaptans  are  known,  some 
of  them  in  well-crystallized  forms.  The  mercury  mercaptides  fur- 
nish an  example  of  these  bodies,  and  are  produced  by  the  action 
of  mercaptans  on  mercuric  oxide,  whence  the  name  of  these  com- 
pounds is  derived  (by  shortening  corpus  mercurio  aptum  to  mer- 


§  59]  THIOETHERS.  79 

captan).  Many  of  the  other  heavy  metals,  such  as  lead,  copper, 
and  bismuth,  yield  mercaptides:  the  lead  compounds  have  a 
yellow  colour.  The  mercaptan  is  liberated  from  all  mercap- 
tides by  the  addition  of  mineral  acids. 

Thioethers. 

59.  In  addition  to  the  methods  given  in  57  for  the  preparation 
of  thioethers,  the  action  of  potassium  sulphide,  K2S,  upon  the  salts 
of  alkylsulphuric  acids  may  be  employed: 

2CJIt[o~sb,K+K,|s  =  (C2H6)2S  +2K2SO4. 

Potassium 
ethylsulphate 

The  thioethers  are  neutral  compounds  with  an  exceedingly  offen- 
sive odour,  eliminated  by  heating  with  copper-powder.  They  are 
liquids  insoluble  in  water,  and  yield  double  compounds  with  metallic 
salts,  such  as  (C2H6)2S.HgCl2. 

With  one  molecule  of  an  alkyl  iodide  the  thioethers  form  remark- 
able crystalline  compounds  of  the  type  (C2H5)3SI.  These  com- 
pounds, called  sulphonium  iodides,  are  readily  soluble  in  water. 
Moist  silver  oxide  replaces  the  I-atom  by  hydroxyl : 

(C2H5)3SI  +  AgOH  =  (C2H5)3SOH  +  AgL 

The  sulphonium  hydroxides  thus  obtained  dissolve  easily  in  water, 
and  are  very  alkaline  in  reaction.  They  are  strong  bases,  absorbing 
carbon  dioxide  from  the  air,  and  yielding  salts  with  acids.  In 
the  sulphonium  halides,  such  as  (C2H5)3S'C1,  sulphur  is  the  only 
element  to  which  the  univalent  alkyl-groups  and  univalent  Cl-atom 
can  be  united,  so  that  these  substances  must  have  constitutional 
formulae  of  the  type 


s 

P  TT  /          \n 
U2±15  Ul 

The  mercaptans  resemble  sulphuretted  hydrogen  in  being  slowly 
oxidized  by  contact  with  air,  whereby  they  are  converted  into  disul- 
phides  like  diethyl  disulphide, 

C2H5°S -S  »C2H5. 
The  hydrogen  linked  to  sulphur  has  been  removed  by  oxidation,  so 


80  ORGANIC  CHEMISTRY.  '  [§  60 

that  the  disulphides  have  the  constitution  given  above.  A  further 
proof  is  their  formation  when  potassium  ethylsulphate  is  heated 
with  potassium  disulphide,  K2S2. 

Numerous  inorganic  compounds  containing  oxygen  and  sulphur 
exist.  Similar  substances  are  also  known  in  organic  chemistry. 

The  sulphoxides,  £nJJ2nM>SO,  are  formed  by  the  oxidation  of 

^n*l2n+i 

thioethers  with  nitric  acid.  Their  constitution  is  indicated  by  the 
fact  that  they  are  very  easily  reduced  to  thioethers.  If  the  oxygen 
were  linked  to  carbon,  they  would  not  behave  in  this  manner,  be- 
cause neither  alcohols  nor  ethers  lose  their  oxygen  by  gentle  reduction. 

The  sulphones  are  compounds  with  the  constitution  r."™21^1  >  SO2, 

t^ntlgn-t-l 

as  shown  in  60.  They  are  formed  by  energetic  oxidation  of  the  thio- 
ethers, and  also  by  oxidizing  sulphoxides.  Nascent  hydrogen  is 
unable  to  effect  their  reduction. 

Sulphonic  Acids. 

60.  The  sulphonic  acids  result  when  mercaptans  undergo  vigorous 
oxidation  (with  nitric  acid).  They  have  the  formula  CnH2n+1  -SOgH. 
During  this  oxidation  the  alkyl-group  remains  intact,  for  the  salts 
of  these  sulphonic  acids  are  also  formed  by  interaction  of  an  alkyl 
iodide  and  a  sulphite: 

C2H5[TTKlSO3K  =  KI +C2H5S03K. 

Since  the  sulphur  in  mercaptans  is  directly  linked  to  carbon,  the 
same  is  true  of  the  sulphonic  acids.  This  is  further  proved  by 
the  fact  that  on  reduction  the  latter  yield  mercaptans.  The  struc- 
ture of  ethylsulphonic  acid  is  therefore  CH3.CH2.SO3H. 

The  group  SO3H  must  contain  a  hydroxyl-group,  because  PC15 
yields  with  a  sulphonic  acid  a  sulphonyl  chloride,  CnH2n  + 1  •  SO2C1, 
from  which  the  sulphonic  acid  may  be  regenerated  by  the  action 
of  water.  The  structure  of  the  compound  is  therefore 

CH3-CH2-S02-OH. 

The  alkylsulphonic  acids  are  strongly  acidic,  very  hygroscopic, 
crystalline  substances,  and  are  very  soluble  in  water. 

In  the  sulphonyl  chlorides,  chlorine  can  be  replaced  by  hydrogen 
in  the  nascent  state.  The  bodies  thus  obtained  have  the  formula 
CnH2n  +  i-SO2H,  and  are  called  sulphinic  acids.  When  an  alkyl 
halide  reacts  with  the  sodium  salt  of  a  sulphinic  acid,  a  sulphone 
(59)  is  formed : 


§  GO]  SULPHONIC  ACIDS.        \  81 

C2H5SO2  Na  +  Br|C2H5  =  £?**•>  SO2  +  NaBr. 

This  mode  of  preparation  is  a  proof  of  the  constitution  of  the 
sulphones. 

Selenium  and  tellurium  compounds  corresponding  to  most  of  these 
sulphur  compounds  are  known,  and  have  afso  a  most  offensive  odour. 


ALKYL-RADICALS  LINKED  TO   NITROGEN. 


I.  AMINES. 

61.  At  the  beginning  of  the  last  chapter  (57)  it  was  stated  that  the 
properties  possessed  by  inorganic  compounds  are  even  more  marked 
in  their  organic  derivatives.  The  compounds  to  be  described  in 
this  chapter  afford  another  striking  example  of  this  phenomenon. 

The  term  amines  is  applied  to  substances  which  may  be  regarded 
as  derived  from  ammonia  by  exchange  of  hydrogen  for  alkyl-radi- 
cals.  The  most  characteristic  property  of  ammonia  is  its  power  of 
combining  with  acids  to  form  salts  by  direct  addition: 

NH3  +  H.X=  NH4.X. 

Tervalent  nitrogen  is  thereby  made  quinquivalent,  a  change  ap- 
parently intimately  connected  with  its  basic  character.  This 
property  is  also  found  among  the  alkylamines.  They  are,  at  least 
those  low  in  the  series,  better  conductors  of  electricity  for  the 
same  molecular  concentration  of  their  aqueous  solutions,  and  are 
therefore  more  strongly  basic  than  ammonia  itself  ("Inorganic 
Chemistry/'  66  and  238).  This  applies  also  to  the  organic  com- 
pounds corresponding  to  ammonium  hydroxide,  NH4OH.  The  last- 
named  substance  is  not  known  in  the  free  state,  but  it  exists  in 
the  aqueous  solution  of  ammonia.  It  is  very  unstable,  being  com- 
pletely decomposed  into  water  and  ammonia  by  boiling  its  solu- 
tion. It  has  only  weakly  basic  properties,  because  there  are  but 
few  NH4-ions  and  OH-ions  in  its  aqueous  solution,  apparently 
because  the  compound  NH4OH  has  a  very  strong  tendency  to 
break  up  into  NH3  and  H2O.  Such  a  decomposition  is,  however, 
no  longer  possible  for  compounds  containing  four  alkyl-groups  in 
place  of  the  four  hydrogen  atoms  of  the  NH^-group,  and  experi- 
ence has  shown  that  these  compounds  possess  great  stability. 
Since  the  nitrogen  cannot  revert  to  the  tervalent  condition,  their 

82 


§§  62,  63]  AMINES.  83 

basic  character,  in  comparison  with  that  of  NH4OH,  is  so  strength- 
ened that  they  are  ionized  to  the  same  degree  as  the  alkalis,  being 
almost  completely  dissociated  in  yi^-normal  solutions. 

The  amines  yield  complex  salts  fully  analogous  to  the  platinum 
salt,  (NH4)2PtCl6,  and  the  gold  salt,  NH4AuCl4,  of  ammonia. 


Nomenclature  and  Isomerism. 

62.  The  amines  are  called  primary,  secondary,  or  tertiary, 
according  to  whether  one,  two,  or  three  hydrogen  atoms  of  NH3 
have  been  exchanged  for  alkyl-radicals.  The  compounds  NR4OH, 
in  which  R  stands  for  an  alkyl-radical,  are  called  quaternary  am- 
monium bases. 

Isomerism  of  the  amines  may  be  due  to  different  causes.  First, 
to  branching  of  the  carbon  chain,  just  as  in  the  alcohols  and  other 
compounds.  Second,  to  the  position  occupied  by  the  nitrogen  in 
the  molecule.  Third,  to  both  causes  simultaneously.  In  addition 
to  these,  the  primary,  secondary,  and  tertiary  nature  of  the  amines 
must  be  taken  into  account.  A  compound  C3H9N,  for  example, 
can  be  propylamine  or  isopropylamine,  CH3-CH2-CH2-NH2  or 

PTT 
,  primary;    methylethylamine,  QH  >NH,  second- 

CH3x 

ary;  or  trimethylamine,  CH3-)N,  tertiary. 
CH/ 


Methods  of  Formation. 

63.  HOFMANN  discovered  that  when  an  alcoholic  or  aqueous 
solution  of  ammonia  is  heated  with  an  alkyl  halide,  the  following 
reactions  take  place: 

I.     CnH2n+1  •  Cl  +  pNH3  =  CnH2n+1  •  NH2,HC1  +(p-l)  NH3. 

The  alkyl  halide  is  added  to  ammonia,  NH3,  a  reaction  analogous 
to  the  formation  of  ammonium  chloride,  NH4C1,  from  ammonia, 
NH3,  and  hydrochloric  acid,  HC1.  Part  of  the  resulting  hydro- 
chloride  is  decomposed  by  ammonia,  with  liberation  of  the 


84  ORGANIC  CHEMISTRY.  [§63 

primary  amine,  the  free  base  reacting  with  the  alky!    halide  in 
accordance  with  equation  II.  : 


II.     CnH2n+1.Cl  +  CnH2n+i-NH2=  (CnH2n+1)2NH,HCL 


Part  of  the  secondary  amine  thus  produced  is  also  set  free,  and 
reacts  according  to  equation  III.: 

III.     CnH2n+1  .  Cl  +  (CnH2n+1)2NH  =  (CnrWO^HCl. 

The  tertiary  amine  is  also  partly  liberated,  and  reacts  with  the 
alkyl  halide  to  yield  the  halide  of  a  quaternary  ammonium  base  : 

IV.     (CnH2n+2)3N  +  CnH2n+1.Gl=  (CnH2n4.1)4N.CL 


It  is  assumed  that  excess  of  ammonia  is  employed;  but  even? 
when  it  is  otherwise,  and  in  general  for  every  proportion  of  alkyl 
halide  and  ammonia,  the  reaction  takes  place  in  these  four  phases. 
The  final  result  is,  therefore,  that  the  primary,  secondary,  and  ter- 
tiary amines,  and  the  ammonium  base,  are  formed  together.  It 
is  often  possible,  however,  so  to  adjust  the  proportion  of  ammonia 
and  alkyl  halide,  together  with  the  duration  of  the  reaction,  etc., 
that  a  given  amine  is  the  main  product,  and  the  quantities  of  the 
other  amines  are  small.  The  nature  of  the  alkyl-group  also  exer- 
cises a  great  influence  upon  the  character  of  the  reaction-product. 

The  separation  of  the  ammonium  bases  from  the  ammonia  and 
amines  is  simple,  because,  while  the  amines  are  liquids  volatilizing: 
without  decomposition,  or  gases,  the  ammonium  bases  are  not  vol- 
atile. When,  therefore,  the  mixture  of  the  amine  hydrohalides 
and  the  ammonium  bases  is  distilled  after  addition  of  caustic 
potash,  only  the  free  amines  pass  over. 

To  separate  the  primary  amines  from  the  mixture  of  the 
hydrohalides  of  the  three  amines,  fractional  crystallization  is  often 
employed  for  the  lower  members,  methylamine,  dimethylamine^ 
and  so  on.  The  propylamines  and  those  succeeding  can  be  sepa- 
rated by  fractional  distillation. 

Various  methods  of  preparing  primary  amines  unmixed  with 
secondary  or  tertiary  are  known  (78,  96,  258,  268,  and  349). 


$  64]  AMINES.  85 

64.  The  velocity  of  the  formation  of  tetraalkylammonium  iodides 
from  triethylamine  and  an  alkyl  iodide  or  bromide  has  been 
investigated  by  MENSCHUTKIN.  It  is  apparently  a  bimolecular 
reaction  ("  Inorganic  Chemistry/7  50)  and  therefore  takes  place 
.according  to  the  equation 


where  s  is  the  velocity,  k  the  constant  of  the  reaction,  a  and  b  the 
quantities  of  amine  and  iodide  per  unit  volume  expressed  in 
molecules,  and  x  the  quantity  of  both  which  has  entered  into 
reaction  after  the  time  t.  Solution  of  this  equation  by  the 
integral  calculus  gives 

b(a-x) 


, 

A/  —  7"?  rr~i<  /\ 


,-, 

a(b  — 


I  standing  for  the  natural  logarithm. 

For  the  investigation  of  these  velocities,  weighed  quantities 
of  the  amine  and  iodide  are  brought  into  contact  in  a  suitable 
solvent,  and  the  solution  heated  in  a  sealed  tube  at  100°,  x  being 
determined  after  the  lapse  of  known  intervals  of  time  t.  The 
value  of  k  is  found  to  be  constant  for  every  reaction:  that  is, 
if  corresponding  sets  of  values  are  substituted  for  t  and  x  in  the 
equation,  on  solving  it  the  same  value  is  always  obtained  for  k. 
The  greater  the  molecular  weight  of  the  alkyl-radical,  the  smaller 
is  k,  although  the  decrease  is  not  very  marked  :  for  example,  when 
the  amine  reacts  with  propyl  bromide,  k  =0*00165;  with  octyl 
"bromide  k  =0*00110  (with  acetone  as  solvent).  The  equation  is 
always  applicable,  being  independent  oHhe  solvent  used,  as  might 
be  expected  from  the  fact  that  it  does  not  contain  any  term 
dependent  upon  the  nature  of  the  solvent.  There  was  made, 
however,  an  unexpected  observation  of  the  extraordinarily  great 
influence  exercised  by  the  nature  of  the  solvent  upon  the  values 
of  k.  Using  hexane  as  a  solvent,  k  =0  •  000180  for  the  combination 
of  triethylamine  and  ethyl  iodide:  for  methyl  alcohol,  on  the 
other  hand,  k  =0-0516,  or  286-6  times  as  great. 

In  many  other  instances  the  nature  of  the  solvent  exercises  an 
important  influence  upon  the  velocity  of  [reaction,  but  a  satis- 
factory explanation  of  the  phenomenon  is  still  lacking. 


86  ORGANIC  CHEMISTRY.  [§65 

Properties. 

65.  The  primary,  secondary,  and  tertiary  amines  are  sharply 
distinguished  from  one  another  by  their  different  behaviour  towards 
nitrous  acid,  HO  -NO. 

Primary  amines  yield  alcohols,  with  evolution  of  nitrogen: 


The  reaction  is  fully  analogous  to  the  decomposition  of  ammonium. 
nitrite  into  water  and  nitrogen: 


NH3.HONO 


[H. 
|  HO 


2H20+N2. 


Secondary  amines  yield  nitrosoamines:    . 

(CnH2n+i)2N[HTHOJNO  =  (CnH2n+])2N.NO+H20. 

The  lower  members  are  yellowish  liquids  of  characteristic  odour, 
and  are  slightly  soluble  in  water.  They  are  easily  reconverted  into 
secondary  amines  by  the  action  of  concentrated  hydrochloric  acid 
(298):  this  is  a  proof  of  the  structure  given  above,  because  if  the 
nitroso-group  were  directly  linked  to  a  carbon  atom  either  by  its 
oxygen  or  by  its  nitrogen,  it  would  not  be  possible  thus  to  recon- 
vert the  nitrosoamine  into  a  secondary  amine. 

Tertiary  amines  are  either  unacted  on,  or  oxidized,  by  nitrous 
acid. 

Their  behaviour  with  nitrous  acid  therefore  affords  a  means  of 
distinguishing  the  three  classes  of  amines  from  one  another.  It 
also  serves  as  a  basis  for  the  separation  of  the  secondary  and  ter- 
tiary amines  in  the  pure  state  from  a  mixture  of  the  two.  When  a 
concentrated  solution  of  sodium  nitrite  is  added  to  a  hydrochloric- 
acid  solution  of  a  mixture  of  the  two  amines,  the  secondary  amine 
is  converted  into  a  nitrosoamine:  this  collects  as  an  oil  on  the  sur- 
face of  the  aqueous  solution,  and  can  be  removed  by  means  of  a 
separa ting-funnel.  The  tertiary  amine  is  not  attacked,  but  re- 
mains in  the  aqueous  solution  in  the  form  of  a  salt:  it  can  be 
obtained  by  distilling  with  caustic  potash.  Any  primary  amine 
present  is  decomposed  during  the  process. 


§66] 


AMINES. 


87 


Another  method  of  distinguishing  between  primary,  secondary, 
and  tertiary  amines  consists  in  the  determination  of  the  number  of 
alkyl-groups  with  which  the  amine  can  combine.  For  example,  if 
a  compound  C3H9N  is  propylamine,  C3H7NH2,  it  should  yield,  when 
heated  with  excess  of  methyl  iodide,  a  compound 


or  if  C3H9N 


(CH3)3 
>NH,     the    same    treatment    should    yield 


C5H14NI:  or  lastly,  if  C3H9N  =  (CH3)3N,  there  would  be 

obtained  (CH3)4NI=C4H12NI.  A  titration  of  the  iodine  ion  of 
the  quaternary  ammonium  iodide  formed  determines  whether 
C3H9N  is  primary,  secondary,  or  tertiary. 

HOFMANN'S  test  for  primary  amines  is  described  in  77. 
Individual  Members. 

66.  The  lower  members  are  inflammable  gases,  and  are  very 
soluble  in  water;  thus,  1150  volumes  of  methylamine  dissolve  in 
one  volume  of  water  at  12  •  5°.  The  succeeding  members  have  low 
boiling-points,  and  are  miscible  with  water  in  all  proportions. 
Both  they  and  the  lower  members  have  a  characteristic  ammo- 
niacal  odour,  like  boiled  lobsters.  The  higher  members  are  odour- 
less and  insoluble  in  water.  The  specific  gravities  of  the  amines 
are  considerably  less  than  1,  that  of  methylamine  being  only  0-699 
at— 11°.  The  following  table  indicates  the  variations  of  their 
boiling-points. 


Alkyl-Radical. 

Primary. 

Secondary. 

Tertiary. 

Methyl 

-6° 

7° 

3-5° 

Ethyl 

19° 

56° 

90° 

n-Propyl  

49° 

98° 

156° 

n-Butyl  

76° 

160° 

215° 

n-Octyl  

180° 

297° 

366° 

Methylamine  occurs  in  Mercurialis  perennis:  it  is  readily  pre- 
pared by  the  interaction  of  ammonia  and  dimethyl  sulphate.  Di- 
methylamine  (299)  and  trimethylamine  are  constituents  of  herring- 
brine. 


88  ORGANIC  CHEMISTRY.  [§67 

Trimethylamine,  (CH3)3N,  can  be  readily  prepared  by  heating 
ammonium  chloride  with  formaldehyde  ("Formalin,"  108)  in  an 
autoclave  at  120°-160°: 

2NH3  +  9CH2O  =  2  (CH3)3N  +  3C02  +  3H20. 

Tetramethylammonium  hydroxide,  (CH3)4N.OH,  is  obtained  by 
treating  a  solution  of  the  corresponding  chloride  in  methyl  alcohol 
with  the  equivalent  quantity  of  caustic  potash.  After  filtering  off 
the  precipitated  potassium  chloride,  the  solution  is  diluted  with 
water,  and  evaporated  in  vacuo  at  35°  to  remove  the  alcohol.  The 
base  crystallizes  out  as  hydrates,  which  are  very  hygroscopic  and 
absorb  carbon  dioxide  readily.  It  is  decomposed  by  heat  into 
trimethylamine  and  methyl  alcohol: 

(CH3)4N.OH  =  (CH3)3N+CH3OH. 

The  higher  ammonium  bases  are  converted  by  dry  distillation 
into  a  tertiary  amine,  water,  and  a  hydrocarbon  CnH2n: 

(C2H5)4N.OH=  (C2H5)3N+C2H4+H20. 

Triethylamine     Ethylene 

The  structure  of  the  ammonium  bases  is  thus  explained.  Only 
the  nitrogen  atom  is  able  to  link  to  itself  the  four  univalent  alkyl- 
groups  and  the  univalent  hydroxyl-group.  It  must  be  assumed 
to  be  quinquivalent  in  these  compounds,  and  the  constitution  of 
the  ammonium  bases  is  therefore 


TT  X^ 

+1  OH 


n,  m,  p,  and  r  being  similar  or  dissimilar. 

Alkyl-derivatives  of  hydrazine  or  diamide,  H2N-NH2,  are  also 
known.  Among  the  methods  for  their  preparation  may  be  men- 
tioned the  direct  introduction  of  an  alkyl-group  into  hydrazine,  and 
the  careful  reduction  of  nitrosoamines  (65).  They  have  little  power 
of  resisting  oxidizing  agents,  reducing  an  alkaline  copper  solution, 
for  example,  at  the  ordinary  temperature. 

67.  Triethylamine  is  soluble  in  water,  although  at  about  20°  this 
solution  separates  into  two  layers.  The  upper  consists  of  a  solu- 
tion of  water  in  the  amine,  and  the  lower  of  a  solution  of  the  amine 


§67] 


AMINES. 


89 


in  water.  In  the  neighbourhood  of  20°  a  slight  rise  in  temperature 
effects  this  separation  into  two  layers,  merely  holding  the  tube  for 
a  short  time  in  the  warm  hand  being  sufficient. 

This  separation  at  a  definite  temperature  is  best  understood 
from  a  consideration  of  the  solubility-curve  of  the  system  amine  + 
water.  This  amine  (Fig.  27)  is  less  soluble  in  warm  water  than  in 


100 

~~7cr~                      D 

90- 

p' 

R'                                           Q' 

l»: 

• 

5  40- 

S  30 

p                r' 

R                                                          *Q 

1 

JO- 

V. 

0 

0      10  '  20      30     40      50     60     70      80     90 

TEMPE8ATU3E 

FIG.  27. — SOLUBILITY-CURVES  FOR  TRIETHYLAMINE  AND  WATER. 


100 

90- 

80- 

70- 

?  60- 

z  50- 

g  40- 

il  so- 

20 

;ao- 

0 


0      10      20      30     40      50      60       70      80      90    100 
TEMPERATURE 

FIG.  28. — USUAL  FORM  OF  SOLUBILITY-CURVE  FOR  Two  LIQUIDS. 

cold,  and  below  20°  is  miscible  with  water  in  all  proportions.  If, 
for  example,  increasing  quantities  of  the  amine  be  added  to  water 
at  30°,  it  dissolves  until  the  amount  of  amine  reaches  about  5  per 
cent.  (cf.  Fig.  27).  The  solution  is  then  saturated,  and  addition  of 
more  of  the  amine  produces  a  second  layer  of  liquid.  On  the  other 
hand,  when  water  is  added  to  triethylamine  at  25°,  it  dissolves 
until  the  amount  of  water  reaches  about  5  per  cent.  (cf.  Fig.  27). 
Beyond  this  point  two  layers  are  formed.  The  line  DC  is  the  solu- 
bility-curve for  water  dissolved  in  triethylamine,  and  the  line  AB 
that  for  triethylamine  in  water.  When  the  temperature  falls,  on 
the  one  hand  the  solubility  of  the  water  in  the  amine  increases,  and 


90  ORGANIC  CHEMISTRY.  [§  67 

on  the  other  that  of  the  amine  in  the  water,  so  that  the  solubility- 
curves  meet  between  B  and  C.  The  whole  area  is  divided  into  two 
parts  by  the  solubility-curves.  All  points  within  ABCD  correspond 
with  two  layers  of  liquid,  and  all  points  outside  it  with  a  homoge- 
neous mixture. 

If,  for  example,  the  abscissa  PQ  is  drawn  for  a  mixture  of. 20  per 
cent,  of  amine  and  80  per  cent,  of  water,  the  mixture  is  homogeneous 
for  all  temperatures  up  to  the  point  R,  and  heterogeneous  above  that 
temperature.  Along  the  very  steep  portion  of  the  curve,  repre- 
sented in  this  special  case  by  the  part  BC,  a  slight  rise  in  tempera- 
ture must  evidently  result  in  separation  of  the  liquid;  because  al- 
though at  about  20°  (the  point  R)  an  80  per  cent,  amine  solution  of 
water  and  a  20  per  cent,  aqueous  solution  of  amine  are  just  about 
to  form,  at  R'  (less  than  1°  higher)  the  separation  would  produce 
an  80  per  cent,  aqueous  solution  of  amine  and  a  20  per  cent,  amine 
solution  of  watffr.  It  follows  that  in  this  part  of  the  curve  a  small 
rise  of  temperature  must  cause  a  separation  of  water  sufficient  to 
alter  the  composition  of  one  of  the  layers  from  20  per  cent,  to  80 
per  cent,  of  amine. 

It  has  been  already  mentioned  that  the  relative  solubility -curve 
for  the  system  water  +  trietliylamme  has  an  abnormal  path  in  the 
portion  BC.  Moreover,  the  whole  curve  differs  from  those  ordi- 
narily obtained.  The  solubility  of  liquids  partially  miscible  with 
one  another  usually  increases  with  the  temperature,  just  as  i-n  the 
case  of  solids  and  liquids,  so  that  the  ordinary  curve  is  therefore  the 
converse  of  that  in  Fig.  27,  and  is  usually  as  represented  in  Fig.  28. 
Very  many  piperidine  (159)  derivatives  belong  to  the  same  type 
as  triethylamine,  and  give  a  similar  curve  of  diminishing  solubility 
in  water. 

The  highest  temperature,  C  (Fig.  27),  at  which  two  liquid  layers 
can  exist  without  being  homogeneous  is  called  the  critical  tempera- 
ture of  solution.  At  this  point  a  rise  of  temperature  renders  the 
entire  liquid  homogeneous;  a  fall  is  accompanied  by  the  formation 
of  minute  drops  in  the  homogeneous  liquid,  due  to  the  reappear- 
ance of  the  second  liquid  layer.  The  point  of  inception  of  turbidity 
caused  by  the  separation  of  the  drops  often  admits  of  very  accurate 
observation.  Since  the  part  ACB  of  the  curve  is  frequently  con- 
siderably flattened,  in  many  instances  a  slight  percentage-change 
in  the  ratio  of  the  amount  of  the  two  liquids  alters  the  critical 
temperature  of  solution  by  less  than  0-1°. 

Addition  of  a  third  substance  in  small  proportion,  however,  has 
a  great  effect  on  the  critical  temperature  of  solution.  For  a  mixture 


§  68]  NITRO-COMPOUNDS.  91 

of  equal  volumes  of  absolute  alcohol  and  petroleum  CRISMER  found 
the  critical  temperature  of  solution  to  be  15 '0°;  O14  per  cent, 
of  water  raised  it  to  17-5°,  and  1-04  per  cent,  to  30-9°.  It  is 
evident  that  the  determination  of  the  critical  temperature  of  solu- 
tion furnishes  a  very  sensitive  process  for  the  detection  and  estima- 
tion of  traces  of  water  in  ethyl  alcohol;  the  same  method  can  be 
applied  to  methyl  alcohol,  acetone,  and  other  substances. 

II.     NITRO-COMPOUNDS. 

68.  When  silver  nitrite  reacts  with  an  alkyl  iodide,  two  com- 
pounds are  formed,  both  with  the  empirical  formula  CuH2n^)NO2, 
but  having  different  boiling-points.  From  ethyl  iodide,  for  ex- 
ample, a  substance  C2H5NO2,  boiling  at  17°,  and  another  boiling 
at  113°-1140,  are  obtained.  The  two  isomerides  are  therefore  read- 
ily separated  by  fractionation. 

The  compound  of  lower  boiling-point  is  decomposed  into  alcohol 
and  nitrous  acid  by  the  action  of  caustic  potash.  It  must  there- 
fore be  looked  upon  as  an  ester  of  nitrous  acid,  being  formed  thus: 


CnH2n+1|I+Ag|.QNO  =  CnH2n+1.ONO  +  AgI. 

When  these  esters,  or  alkyl  nitrites,  are  reduced,  they  are  con- 
verted into  an  alcohol  and  ammonia. 

The  compound  boiling  at  the  higher  temperature  behaves  quite 
differently.  It  is  not  converted  into  a  nitrite  and  alcohol  by  the 
action  of  alkalis,  and  on  reduction  its  two  oxygen  atoms  are  replaced 
by  two  hydrogen  atoms,  with  formation  of  a  primary  amine. 

CnH2n+1N02^CnH2n+1NH2. 

The  last  reaction  shows  that  the  nitrogen  in  this  class  oi 
compounds  is  directly  linked  to  carbon,  because  it  is  so  in  the 
amines.  The  oxygen  atoms  can  be  linked  only  to  the  nitrogen, 
because  the  reduction  to  amine  takes  place  at  the  ordinary  tem- 
perature. Under  these  conditions  it  is  not  possible  to  replace 
oxygen  directly  linked  to  carbon,  for  neither  alcohols  nor  ethers 
are  reduced  at  low  temperatures  to  substances  not  containing 
oxygen.  This  leads  to  the  conclusion  that  these  substances,  called 
nitro-compounds,  have  the  constitution  CnH2n+1 — N02. 

Nitro-compounds  therefore  contain  a  group  N02,  the  nitrogen  atom, 
being  directly  linked  to  carbon;  this  group  is  called  the  nitro-group. 


92  ORGANIC  CHEMISTRY.  [§§  69 

The  generation  of  nitrite  and  nitro-compound  may  be  explained 
by  assuming  the  production  of  the  nitrite  to  be  a  regular  ionic 
reaction,  and  that  of  the  nitro-compound  to  be  preceded  by  the 

Ag-O-N-O 
formation    of    an    addition-product,  /\      ,    subsequently 

I       C2H5 
decomposed  with  fission  of  silver  iodide. 

It  has,  in  fact,  been  stated  that  a  dilute,  aqueous  solution  of 
potassium  nitrite  is  converted  by  dimethyl  sulphate  into  methyl 
nitrite  only,  but  that  a  concentrated  solution  yields  up  to  25  per 
cent,  of  nitromethane. 

The  names  of  these  compounds  are  formed  from  those  of  the 
saturated  hydrocarbons  by  means  of  the  prefix  nitro.  The  com- 
pound CH3NO2  is  thus  nitromethane;  C2H5NO2  is  nitroethane;  and 
so  on.  The  members  of  this  homologous  series  are  called  nitro- 
paraffins.  They  are  colourless  liquids  of  ethereal  odour:  the  lower 
members  are  slightly  soluble  in  water.  They  all  distil  without 
decomposition. 

69.  The  nitro-derivatives  have  a  number  of  characteristic  pro- 
perties, among  them  the  possession  of  one  hydrogen  atom  replaceable 
by  alkali-metals,  especially  sodium.  This  sodium  compound  is  most 
readily  obtained  by  the  action  of  sodium  ethoxide  or  methoxide  upon 
the  nitro-compound  in  absolute-alcoholic  solution.  A  fine,  white, 
crystalline  precipitate  is  thus  formed,  that  from  nitroethane,  for 
example,  having  the  composition  C2H4NaNO2.  The  insolubility 
of  these  sodium  compounds  in  absolute  alcohol  is  sometimes  em- 
ployed in  the  separation  of  the  nitroparaffins  from  other  substances. 
This  power  of  exchanging  hydrogen  for  sodium  only  exists 
when  at  least  one  hydrogen  atom  is  linked  to  the  carbon  atom 
carrying  the  nitro-group.  As  from  nitroethane,  a  metallic  com- 
pound is  obtained  from  secondary  nitropropane, 

CH3.CH 
but  tertiary  nitrobutane, 


CH3/ 

does  not  yield  any  corresponding  metallic  derivative.    The  struc- 
ture of  these  metallic  compounds  is  considered  in  291. 

When  an  alkaline  solution  of  a  nitro-compound  is  brought  into 


§  70]  NI TRO-COMPO  UNDS.  93' 

contact  with  bromine,  one  (or  more)  of  its  hydrogen  atoms  linked 
to  the  same  carbon  atom  as  the  nitro-group  is  replaced  by  bromine. 
This  reaction  is  analogous  to  the  substitution  by  metals,  it  being 
still  possible,  for  example,  to  introduce  one  bromine  atom  into 

/Br 
CH3.CHBrN02,  but  not  into  CH3.C^-CH3 

\NO2. 

70.  The  behaviour  of  nitro-compounds  with  nitrous  acid  is  very 
characteristic,  and  affords  a  method  of  distinguishing  between  pri- 
mary, secondary,  and  tertiary  nitre-derivatives.  The  reaction  is  car- 
ried out  by  adding  sodium  nitrite  to  an  alkaline  solution  of  the 
nitre-compound,  and  acidifying  with  dilute  sulphuric  acid.  From 
a  primary  nitro-compound,  an  alkylnitrolic  acid  is  formed: 


ii  v/2 
Ethylnitrolic  acid 

The  constitution  of  these  compounds  is  indicated  by  their  produc- 
tion from  a  dibromonitro-compound  by  the  action  of  hydroxylamine,, 
H2NOH: 


CH3.C|Br,  +  H,|NOH  -  CH 

\~ 

XN02 

The  alkylnitrolic  acids  dissolve  in  alkalis,  yielding  metallic  com- 
pounds of  blood-red  colour,  this  reaction  affording  a  characteristic 
test  for  them.  They  crystallize  well,  but  are  by  no  means  stable, 

When  similarly  treated,  the  secondary  nitro-compounds  yield 

pseudonitroles.  They  contain  the  group  =* 

p    NO 
CH3>(  <NO, 

Propylpseudonitrole. 

When  solid,  the  pseudomtroles  are  colourless,  crystalline  sub* 
stances,  but  have  an  intense  blue  colour  in  the  fused  state  or  in 
solution.  This  characteristic  serves  as  a  test  for  them. 

Lastly,  the  tertiary  nitro-compounds  are  not  acted  on  by  nitrous 
acid. 

Among  the  other  properties  of  nitro-compounds  is  their  decom- 
position into  the  acid  with  the  same  number  of  carbon  atoms  and 
hydroxylamine,  by  heating  with  hydrochloric  acid: 


CH3-CH2.NO2 

Nitroethane  Acetic  acid     Hydroxylamine 


94  ORGANIC  CHEMISTRY.  [§  70 

The  mechanism  of  this  reaction  is  explicable  on  the  assumption  that 
the  nitro-com  pound  is  first  transformed  into  a  hydroxamic  acid  ; 


R.CH2NO2  ->  R-C  ^ 

Hydroxamic  acid 

The  hydroxamic  acid  is  then  converted  by  the  water  present  into 
the  acid  and  hydroxylamine  : 

=R'C^  OH 

Acid         Hydroxylamine 


ALKYL-RADICALS  LINKED  TO   OTHER  ELEMENTS. 

I.  ALKYL-RADICALS  LINKED  TO  ELEMENTS  OF  THE  NITROGEN 

GROUP. 

71.  Ammonia  unites  readily  with  acids,  with  formation  of  salts. 
Phosphine,  PH3,  also  possesses  this  property,  although  the  phos- 
phonium  salts,  PH4X,  are  decomposed  even  by  water  into  an  acid 
and  phosphine. 

The  basic  character  has  wholly  disappeared  in  arsine,  AsH3, 
and  stibine,  SbH3.  Bismuth  does  not  yield  a  hydride,  and  possesses 
only  very  slight  traces  of  the  characteristics  of  metalloids. 

Ammonia  cannot  be  easily  oxidized,  and  is  unacted  on  by  the 
oxygen  of  the  atmosphere  at  ordinary  temperatures.  On  the 
other  hand,  the  hydrides  of  phosphorus,  arsenic,  and  antimony  are 
readily  oxidized. 

All  these  properties  are  displayed  by  the  compounds  of  these 
elements  with  alkyl-radicals. 

Phosphines. 

72.  The  amines  yield  stronger  bases  than  ammonia.  Similarly, 
the  phosphines  form  stronger  bases  than  phosphine.  In  both  cases 
this  property  becomes  more  marked  as  the  number  of  alkyl-groups 
replacing  hydrogen  atoms  increases.  The  salts  of  the  monoalkyl- 
phosphines,  for  example,  are  decomposed  by  water,  whereas  those 
of  the  dialkylphosphines  and  trialkylphosphines  are  not.  The 
quaternary  phosphonium  bases,  PR..OH,  are  as  strongly  basic  as 
the  ammonium  bases.  When  a  phosphonium  base  is  heated,  it 
does  not,  like  an  ammonium  base  (66),  decompose  into  an  alcohol 
(or  CnH2n  -f  H?O)  and  a  trialkyl  base,  but  into  a  hydrocarbon 
and  an  oxygen  compound  : 


95 


96  ORGANIC  CHEMISTRY.  [§73 

This  substance  is  called  triethylphosphine  oxide.  In  this  reaction 
the  great  affinity  between  phosphorus  and  oxygen  plays  an  impor- 
tant part.  This  affinity  is  also  indicated  by  the  ease  with  which  the 
phosphines  undergo  oxidation,  a  change  effected  even  by  the  action 
of  the  air.  Nitric  acid  oxidizes  phosphine,  PH3,  to  phosphoric 
acid,  OP(OH)3:  in  an  analogous  manner  the  phosphines  take  up 
one  oxygen  atom,  and  in  addition  as  many  oxygen  atoms  as  there 
are  hydrogen  atoms  directly  linked  to  phosphorus: 


3  P-O 
(HO),     °' 

Monomethylphosphinic  Dimethylphosphinic 

acid  acid 

and     (CH3)3P      gives          (CH3)3P:O. 

Trimethylphosphine  oxide 

The  constitution  of  these  compounds  is  established  by  a  variety 
of  considerations:  for  instance,  by  the  fact  that  the  monoalkylphos- 
phinic  acids  are  dibasic,  that  the  dialkylphosphinic  acids  are 
monobasic,  and  that  the  trialkylphosphine  oxides  have  no  acidic 
properties. 

The  phosphines  are  colourless  liquids  of  penetrating,  stupefying 
odour.  Methylphosphine,  CH3PH2,  is  a  gas:  in  very  small  quan- 
tities triethylphosphine  has  an  odour  of  hyacinths. 

Methods  of  Formation.  —  Only  tertiary  phosphines  and  phospho- 
nium  compounds  are  formed  by  the  action  of  alkyl  halides  upon 
phosphine,  PH3.  Primary  and  secondary  phosphines  are  obtained 
by  heating  phosphonium  iodide,  PHJ,  with  an  alkyl  iodide  and 
zinc  oxide. 


Arsines. 

73.  The  primary  and  secondary  ar sines,  H2AsCH3  and  HAs(CH3)2, 
are  obtained  by  reduction  of  monomethylarsinic  acid  and  dimethyl- 
arsinic  acid,  (CH3)HAsO-OH  and  (CH3)2AsO-OH,  by  amalgamated 
zinc-dust  and  hydrochloric  acid.  Both  are  immediately  oxidized 
by  the  air.  Tertiary  arsines  do  not  yield  bases  with  water.  They 
are  formed  by  the  action  of  a  zinc  alkide  on  arsenic  chloride,  AsCl3, 
and  from  sodium  arsenide  and  an  alkyl  iodide : 

AsNa3  +  3C2H5I   ==  As(C2H5)3  +  3NaI. 

Quaternary  arsonium  bases,  however,  have  strongly  marked  basic 
properties.  They  are  prepared  by  the  addition  of  alkyl  halides  to 


•§  74]  ST I  BINES  AND  BISMUTHINES.  97 

tertiary  arsines,  and  treatment  of  the  resulting  halide  with,  silver 
hydroxide. 

The  best-known  arsenic  derivatives  containing  alkyl-radicalsare 
the  cacodyl  compounds.  They  were  investigated  by  BUNSEN,  who  gave 
them  this  name  in  consequence  of  their  offensive  smell.  They  are 
very  poisonous.  The  name  cacodyl  is  applied  to  the  univalent  group 

PH 
;          £jj3>As— .     Cacodyl  oxide,  [(CH3)2As]2O,   is  formed  by  distilling 

arsenious  oxide  with  the  acetate  of  an  alkali-metal.  .All  the  other 
cacodyl  compounds  are  obtained  from  cacodyl  oxide;  thus,  cacodyl 
chloride,  (CH3)2AsCl,  is  prepared  by  heating  the  oxide  with  hydro- 
chloric acid,  and  cacodyl,  (CH3)2As»As(CH3)a,  by  heating  the  chlo- 
ride with  zinc  in  an  atmosphere  of  carbon  dioxide.  When  brought 
into  contact  with  air,  both  ignite  spontaneously. 

Stibines  and  Bismuthines. 

The  tertiary  stibines  and  the  quaternary  stibonium  bases  have  been 
obtained  from  antimony.  The  first-named  are  very  readily  oxidized, 
taking  fire  spontaneously  in  the  air.  The  stibonium  bases  are  as 
basic  in  character  as  the  correspcniing  nitrogen,  phosphorus,  and  ar- 
senic derivatives.  The  pentamethy  -dirivztivs  Sb  (CH3)s  is  also  known. 

Bismuth  does  not  yield  a  hydride,  but  tertiary  bismuthines,  such 
as  (C2H5)3Bi,  have  been  prepared.  They  are  very  unstable,  arid 
explode  when  heated.  They  do  not  form  addition-products  with 
alkyl  halides,  so  that  the  "  bismuthonium  "  bases  are  unknown. 

M.  ALKYL-RADICALS  LINKED  TO  THE  ELEMENTS  OF  THE  CARBON 

GROUP. 

74.  The  elements  in  each  group  or  column  of  the  periodic  system 
are  divided  into  two  sub-groups:  in  one  the  elements  are  electro- 
positive and  base-forming;  in  the  other  electro-negative  and  acid- 
forming  (''Inorganic  Chemistry,"  213).  In  the  first  division  of  the 
carbon  group  are  titanium,  zirconium,  and  thorium ;  in  the  second, 
carbon,  silicon,  germanium,  tin,  and  lead.  Only  elements  belonging 
to  electro-negative  sub-groups  are  capable  of  yielding  alkyl-compounds, 
this  being  true  not  only  of  the  carbon  group  of  elements,  but  also 
of  the  elements  of  the  other  groups.  In  1870,  MENDELEEFF  for 
this  reason  predicted  that  the  then  unknown  element  germanium 
would,  in  accordance  with  its  position  in  the  periodic  system,  yield 
.alkyl-derivatives;  this  prediction  was  confirmed  by  the  researches 
•of  WINKLER,  to  whom  science  is  indebted  for  the  discovery  of  this 


98  ORGANIC  CHEMISTRY.  [§74 

element.  Titanium  belongs  to  the  electro-positive  sub-group,  and 
though  in  many  respects  it  resembles  silicon,  it  has  not  been 
possible  to  prepare  its  alkyl-derivatives. 

Like  carbon,  the  elements  silicon,  germanium,  tin,  and  lead  are 
quadrivalent.  Numerous  attempts  have  been  made  to  prepare  com- 
pounds containing  chains  of  silicon  atoms  resembling  the  carbon 
chains.  They  have  not  been  successful,  no  compounds  containing  a 
chain  of  more  than  three  silicon  atoms  having  been  prepared.  As 
far,  therefore,  as  is  at  present  known,  silicon  lacks  the  power  of  form- 
ing long  chains  like  those  present  in  many  carbon  compounds.  On 
account  of  this  defect,  a  "Chemistry  of  Silicon,"  analogous  to  the 
" Chemistry  of  Carbon,"  is  not  possible. 

The  silicon  alkides,  or  silicanes,  have  a  character  analogous  to 
that  of  the  similarly  constituted  alkyl-derivatives  of  carbon.  For 
example,  silicon  tetraethide,  Si(C2H5).i,  and  tetraethylmethane,  C(C2H5)4, 
are  known.  Both  are  liquids,  and  are  not  acted  upon  by  either 
fuming  nitric  acid  or  fuming  sulphuric  acid  at  ordinary  tempera- 
tures, but  yield  substitution-products  with  chlorine.  Silicohep- 
tane,  (C2H5)3SiH,  has  a  petroleum-like  odour,  a  resemblance  to  tri- 
ethylmethane,  (C2H5)3CH. 


Optically  Active  Compounds  with  Asymmetric  Atoms  Other  Than 

Carbon. 

The  existence  of  optical  activity  occasioned  by  the  presence 
of  asymmetric  atoms  of  elements  other  than  carbon  has  been 
established  by  several  researches.  Asymmetric  sulphonium 
compounds  of  the  type 

RI\       /Ra 

S 
R/"    \)H 

are  known,  with  optical  activity  caused  by  the  presence  of  an 
asymmetric,  quadrivalent  sulphur  atom. 

POPE  has  resolved  into  optically  active  components  nitrogen 
compounds  of  the  type 

NR1R2R3R4X, 

in  which  X  represents  an  acid-radical,   the  activity  being  due 
to  an  asymmetric  nitrogen  atom. 


§74] 


ASYMMETRIC   MOLECULAR   STRUCTURE. 


99 


He  prepared  the  salt  of  the  strongly  optically  active  d-cam- 
phorsulphonic  acid  with  the  base  methylallylphenylbenzylammo- 
nium  hydroxide, 

HO  •  N  (CH.)  (C3H5)  (C6H5)  (C6H5  •  CH2) , 

and  crystallized  it  fractionally  from  acetone,  a  solvent  less  likely 
to  cause  decomposition  than  those  with  a  hj-droxyl-group.  By 
this  means  he  succeeded  in  resolving  the  base  into  its  dextro- 
rotatory and  Isevo-rotatory  components.  POPE  has  resolved  simi- 
larly the  sulphonium  compound  (195), 

HO  •  S  (CH3)  (C2H5)  (CH2  -  COOH) . 

Although  the  tetrahedron-grouping  is  assigned  to  compounds 
with  a  quadrivalent,  asymmetric  atom  such  as  carbon,  there  is 


D  .0 

FIG.  29. — ASYMMETRIC  MOLECULAR  STRUCTURE. 

no  general  agreement  as  to  the  position  and  the  direction  of  the 
linkings  of  the  quinquivalent,  asymmetric  nitrogen  atom. 

WERNER'S  researches  also  support  the  hypothesis  that  any 
asymmetric  molecular  structure  occasions  optical  activity.  He 
assumes  ("  Inorganic  Chemistry/'  323)  in  the  complex  cobalt 
derivatives  direct  union  of  six  atoms  or  groups  to  the  metallic 
atom,  and  regards  them  as  situated  at  the  angles  of  a  regular 
octahedron,  with  the  metallic  atom  at  its  centre.  Various 
groupings  giving  mirror-images  incapable  of  being  superimposed 
are  possible;  he  succeeded  in  preparing  such  compounds,  and  by 
combination  with  an  optically  active  acid,  such  as  bromocamphor- 
sulphonic  acid,  in  resolving  them  into  their  optically  active 
components. 


100  ORGANIC  CHEMISTRY.  [§  75 

Organic  compounds  of  tin  containing  a  tin  atom  linked  to  four 
dissimilar  groups,  and  therefore  possessing  an  asymmetric  tin  atom, 
have  been  prepared  by  POPE.  He  has  also  succeeded  in  resolving 
these  derivatives  into  their  optically  active  components,  and  KIPPINQ 
has  effected  the  resolution  of  asymmetric  silicon  compounds,  proofs 
that  optical  activity  does  not  depend  on  the  nature  of  the  carbon 
atom,  but  is  inherent  in  every  asymmetric  arrangement  of  groups 
round  a  central  atom. 

III.  METALLIC   ALKIDES. 

75.  When  excess  of  ethyl  iodide  is  warmed  with  zinc,  a  white 
crystalline  compound,  C2H5ZnI,  is  formed,  and  on  stronger  heat- 
ing it  yields  zinc  ethide,  Zn(C2H5)2,  and  zinc  iodide: 

2C2H5ZnI  =  Zn(C2H5)2+ZnI2. 

Zinc  ethide  can  be  separated  by  distillation,  which  must  be  per- 
formed in  an  apparatus  filled  with  an  inert  gas,  because  this  com- 
pound, like  the  other  zinc  alkides,  burns  spontaneously  when  ex- 
posed to  air. 

The  metallic  alkides  are  colourless  liquids,  heavier  than  water. 
Zinc  methide  boils  at  46°,  zinc  ethide  at  118°,  and  zinc  propide  at 
146°. 

When  an  alkyl  iodide  reacts  with  a  zinc  alkide,  a  saturated 
hydrocarbon  is  formed: 

=  ZnI2+2CH3.CH3. 

Water  converts  zinc  alkides  into  saturated  hydrocarbons  and 
zinc  oxide: 

Zn(CH3)2+H20  =  2CH4+ZnO. 

The  halogens  react  very  energetically  with  zinc  alkides,  yielding 
alkyl  halides. 

Sodium  alkides  and  potassium  alkides  are  formed  by  the  action 
of  sodium  and  potassium  respectively  upon  zinc  alkides.  These 
metals  dissolve  in  zinc  alkides,  precipitating  an  equivalent 
quantity  of  zinc.  Sodium  alkides  and  potassium  alkides  have  not 
been  obtained  in  the  pure  state,  but  only  in  solution  in  zinc  alkides. 

Very  remarkable  compounds  of  magnesium  have  been  obtained 
by  GRIGNARD.  When  magnesium-turnings  are  brought  into  con- 


§  75]  METALLIC   ALKIDES.  101 

tact  with  a  dry  ethereal  solution  of  an  alkyl  iodide,  one  gramme- 
molecule  of  the  latter  being  employed  for  each  gramme-atom  of 
magnesium,  a  reaction  ensues,  the  heat  evolved  raising  the  ether  to 
the  boiling-point.  When  sufficient  ether  is  present,  all  the  mag- 
nesium dissolves,  forming  an  alkyl  magnesium  iodide,  CnH2n+1  -Mg-I. 
This  is  combined  with  one  molecule  of  ether,  because  on  evap- 
oration to  dry  ness  the  residua  still  contains  equi  molecular  propor- 
tions of  ether  and  the  metallic  compound. 

The  alkyl  magnesium  halides  of  the  type  R-Mg-X  can  also  be 
obtained  free  from  ether  by  dissolving  the  alkyl  halide  in  benzene, 
light  petroleum,  and  other  solvents,  adding  magnesium,  and  induc- 
ing the  reaction  by  the  introduction  of  a  small  quantity  of  a  ter- 
tiary amine  or  of  ether  as  a  catalyst. 

Unlike  the  zinc  alkides,  the  alkyl  magnesium  halides  do  not 
ignite  spontaneously  when  brought  into  contact  with  air.  They 
are  often  employed  for  syntheses,  notably  those  of  the  secondary 
and  tertiary  alcohols  (102). 

The  alkyl  magnesium  halides  are  decomposed  by  water,  with 
formation  of  saturated  hydrocarbons: 

CnH2n+1  .Mg.Cl+H20  =  CnH2n+2  + Mg(OH)Cl. 

Mercury  alkides  are  prepared  similarly  to  zinc  alkides.  They 
do  not  ignite  in  the  air,  are  not  attacked  by  water,  and  are  danger- 
ously poisonous.  Such  compounds  as  C2H6»Hg.OH  are  weak 
bases. 

Alkyl-derivatives  of  beryllium,  magnesium,  cadmium,  alumin- 
ium, thallium,  and  lead  have  also  been  obtained,  some  by  the  aid 
of  GRIGNARD'S  alkyl  magnesium  halides.  A  typical  instance  is  the 
formation  of  tin  ethide  by  the  interaction  of  stannic  bromide  and 
ethyl  magnesium  bromide: 

SnBr4  +4C2H5  •  Mg .  Br  =  Sn(C2H6)4  +4MgBr2. 


NITRILES  AND  ISONITRILES. 

76.  When  potassium  ethylsulphate  is  distilled  with  potassium 
cyanide  or  anhydrous  potassium  ferrocyanide,  K4Fe(CN)6,  a  liquid 
of  exceedingly  unpleasant  odour  is  obtained.  By  fractional  distil- 
lation it  can  be  separated  into  two  substances,  both  with  the  formula 
C3H5N.  One  is  called  ethylcarbylamine,  and  is  only  present  in 
small  proportion:  it  boils  at  82°,  and  has  a  disagreeable  smell  like 
that  of  the  original  mixture.  The  other  constitutes  the  main  por- 
tion, and  is  called  ethyl  cyanide:  it  boils  at  97°,  and  after  purifica- 
tion has  a  not  unpleasant  odour,  which  is  much  less  penetrating 
than  that  of  ethylcarbylamine. 

When  acted  upon  by  inorganic  acids,  these  isomerides  yield  quite 
different  decomposition-products.  Ethylcarbylamine  is  attacked 
at  ordinary  temperatures:  the  oily  layer  floating  on  the  surf  ace  of 
the  acid  dissolves  completely,  and  the  disagreeable  odour 
disappears.  Formic  acid,  CH2O2,  can  be  obtained  from  this 
solution  by  distillation;  and  on  addition  of  caustic  potash  to  the 
residue  in  the  distilling-flask  and  subsequent  distillation,  ethyl- 
amine,  C2H5NH2,  passes  over,  indicating  that  the  nitrogen  atom 
in  ethylcarbylamine,  C3H5N,  is  directly  united  with  the  ethyl- 
group: 

C3H5N  +  2H2O = CH2O2 + C2H5NH2. 

Ethylcarbylamine  Formic  acid     Ethylamine 

Ethyl  cyanide  is  only  slowly  attacked  by  inorganic  acids  at 
ordinary  temperatures,  but  heating  accelerates  their  action.  On 
warming  the  mixture  in  a  flask  with  a  reflux-condenser  and  subse- 
quent distillation,  propionic  acid,  C3H6O2,  passes  over.  This  acid 
contains  the  same  number  of  carbon  atoms  as  ethyl  cyanide,  C3H5N. 
On  making  the  residue  in  the  flask  alkaline  and  again  distilling, 
ammonia  is  obtained.  The  nitrogen  atom  in  ethyl  cyanide  cannot, 
therefore,  be  in  direct  union  with  the  ethyl-group: 

C3H5N+2H20  =  C3H602  +  NH3. 

Eihyl  cyanide  Propionic  acid 

102 


§  77]  NITRILES  AND   isoNITRILES.  103 

These  facts  indicate  that  the  nitrogen  atom  in  ethylcarbylamine 
is  in  direct  union  with  the  ethyl-group,  and  that  the  three  carbon 
atoms  are  not  directly  united,  since  one  of  them  can  be  eliminated 
with  production  of  formic  acid.  In  ethyl  cyanide,  on  the  other 
hand,  there  must  be  a  chain  of  three  carbon  atoms  like  that  in 
propionic  acid  (80),  and  the  nitrogen  cannot  be  directly  linked  to 
the  ethyl-group.  These  facts  are  expressed  by  the  constitutional 
formulse 

I.  C2H5— NC,        II.  C2H5— CN. 

Carbylamine  Cyanide 

On  account  of  their  method  of  formation,  each  must  contain  the 
group  CN. 

Compounds  with  a  structural  formula  like  I.  are  named  carbyl- 
amines or  isonitriles;  those  with  a  structural  formula  like  II. are  called 
cyanides  or  nitrites.  The  names  of  the  former  are  derived  from 
the  alkyl-radical  they  contain,  thus  methylcarbylamine,  ethylcar- 
bylamine, etc.  The  latter  can  be  designated  analogously  methyl 
cyanide,  ethyl  cyanide,  etc.,  but  are  usually  called  nitrites  and  are 
named  after  the  acid  from  which  they  are  derived.  Thus  CH3-CN 
is  acetonitrile ,  and  C2H5-CN  propionitrile,SLndso  on. 

The  constitution  of  the  groups  — CN  and  — NC  requires  further 
consideration.  They  are  represented  as  — C^rN  and  — N^=C, 
the  first  with  a  triple,  and  the  second  with  a  double,  bond 
between  C  and  N  (cf.  119). 

In  NEP'S  view,  the  carbylamines  furnish  one  of  the  few  examples 
of  compounds  with  a  bivalent  carbon  atom.  He  proved  the  formula 
R.N:C  to  represent  the  constitution  of  the  carbylamines  by 
demonstrating  that  addition  of  halogens,  hydrogen  halides,  sulphur, 
and  other  substances  only  takes  place  at  the  carbon  atom,  with 
formation  of  compounds  of  the  type  R.NCX2,  R-NCHX,  R.NCS, 
and  so  on  (cf.  130  and  261). 

Carbylamines. 

77.  Carbylamines  are  the  principal  product  of  the  interaction 
of  alkyl  iodides  and  silver  cyanide.  They  can  also  be  obtained 
unmixed  with  nitriles  by  the  action  of  caustic  potash  and  chloro- 
form, CHC13,  upon  primary  amines: 


104  ORGANIC  CHEMISTRY  [§  78 

On  account  of  the  disagreeable  and  characteristic  odour  of  the 
carbylamines,  this  reaction  affords  an  exceedingly  delicate  test  for 
primary  amines.  Secondary  and  tertiary  amines  are  not  converted 
into  carbylamines  by  this  reaction,  since  they  lack  two  hydrogen 
atoms  in  direct  union  with  the  nitrogen  atom  of  the  amine. 

The  carbylamines  are  colourless  liquids,  very  stable  towards 
alkalis,  but  readily  converted  by  acids  into  a  primary  amine  and 
formic  acid.  With  dry  hydrochloric  acid  in  ethereal  solution 
they  yield  unstable  addition-products,  such  as  2CH3NC«3HC1. 

Nitriles. 

78.  Nitriles  are  the  chief  product  obtained  when  potassium 
cyanide  reacts  with  alkyl  iodides  (cf.  77),  or  when  it  is  submitted 
to  dry  distillation  with  potassium  alkylsulphate.  Sometimes 
anhydrous  potassium  ferrocyanide,  K4Fe(CN)6,  can  be  advan- 
tageously substituted  for  potassium  cyanide. 

Nitriles  can  be  prepared  by  the  action  of  an  alkaline  bromine 
solution  (German,  Bromlauge)  on  the  higher  primary  amines: 

C7H15CH2  .  NH2  +2Br2  +2NaOH  =  C7H15CH2  .  NBr2  +2NaBr  +2H20; 
HNBrI  +2NaOH  =  C7Hlf£N  +2NaBr  +2H20. 


Other  methods  of  preparation  are  mentioned  in  96  and  103. 

The  nitriles  are  liquids  of  characteristic  odour,  soluble  in  water,, 
and  having  specific  gravities  about  0-8.  They  are  converted  not 
only  by  acids,  but  also  by  warming  with  alkalis,  into  fatty  acids 
containing  the  same  number  of  carbon  atoms  and  ammonia,  a 
process  called  hydrolysis.  They  form  addition-products  with  many 
substances,  by  conversion  of  the  triple  bond  between  nitrogen  and 
carbon  into  a  single  bond.  An  example  of  this  reaction  is  the 
addition  of  nascent  hydrogen  (MENDIUS)  : 

C2H5-CN+4H  =  C2H5.CH2.NH2. 

This  produces  a  primary  amine  (63)  with  the  same  number  of 
carbon  atoms  as  the  nitrile,  the  yield  being  very  good  for  the 
higher  members  when  sodium  is  brought  into  contact  with  a 
mixture  of  the  nitrile  and  boiling  absolute  alcohol. 

A   description    of  a  number  of  other  addition-products  of  the- 
nitriles  is  given  in  97. 


ACIDS,  CnH2n02. 

79.  A  solution  of  a  sodium  alkide  in  zinc  alkide  is  obtained  by 
the  interaction  of  sodium  and  a  zinc  alkide  (75) .  When  a  stream 
of  dry  carbon  dioxide  is  passed  into  this  solution,  the  sodium  salt 
of  an  acid  with  one  carbon  atom  more  in  the  molecule  than  the 
alkyl-group  is  formed.  Thus,  sodium  methide,  CH3Na;  yields 
sodium  acetate,  C2H3O2Na.  This  reaction  may  be  explained  by 
assuming  that  the  sodium  atom  is  released  from  the  alkyl-group,  and 
reacts  with  CO2,  becoming  linked  to  an  oxygen  atom,  an  element 

for  which  it  possesses  great  affinity:  C^     is  thus  converted  into 

— C^QXT  .     Since   this  group,   and   also   the   alkyl-radical  from 

which  the  sodium  atom  has  been  separated,  have  one  free  carbon 
bond  apiece,  it  may  be  assumed  that  the  two  groups  unite,  forming 
a  compound 

CTT  f\s£\J 

n^n-Hl 


Analogous  to  this  is  the  formation  of  acids  by  the  interaction 
of  GRIGNARD'S  alkyl  magnesium  haiides  (75)  and  carbon  dioxide: 

CH3.Mg.Br+CO2  =  CH3.CO.O.Mg.Br. 

Addition-product 

The  addition-product  is  decomposed  by  water,  with  production  of 
the  acid  : 

CH3.CO.O.Mg.Br  +  H2O  =  CH3.CO.OH+Mg(OH)Br. 

In  accordance  with  these  reactions  the  acids    CnH2nO2  contain 
the  group  —  C<J         m  union  with  an  alkyl-radical.     This  view  is 


supported  by  the  formation  of  these  compounds  by  other  methods. 

Among  them  is  their  synthesis  by  the  interaction  of  an  alkyl  iodide 
and  potassium  cyanide,  followed  by  hydrolysis  of  the  resulting  nitnle. 
This  hydrolysis  consists  in  the  addition  of  the  elements  of  water, 

105 


106  ORGANIC  CHEMISTRY.  [§  79 

and  entails  breaking  the  bonds  between  carbon  and  nitrogen  in  the 
group  —  C=N.  If  any  otherbond  inanitrileCH3.CH2.CH2  .  .  .  .  CN 
were  released,  it  would  involve  a  severance  of  the  carbon 
chain,  and  prevent  the  formation  of  an  acid  containing  the  same 
number  of  carbon  atoms  as  the  nitrile.  The  hydrolysis  of  the 
nitrile,  in  which  an  acid  and  ammonia  are  formed,  may  therefore 
•be  explained  by  assuming  that  the  molecules  of  water  are  resolved 
into  H  and  OH,  the  hydroxyl  uniting  with  the  carbon,  and  the 
hydrogen  with  the  nitrogen.  By  a  threefold  repetition  of  this  the 
nitrogen  is  converted  into  ammonia,  the  three  bonds  between  car- 
bon and  nitrogen,  in  the  nitrile,  being  severed: 

/OH    H\ 
CH3.C(-OH    H-9N. 
\OH    H/ 

The  formula  of  the  acid  formed  is  not  CH3.CO3H3,  but 
CH3.CO2H,  containing  one  molecule  of  water  less.  When  one 
molecule  of  water  is  eliminated  from  CH3-CO3H3,  there  results 


CH3-C|OH  —,  CH3-C^Qjj,  a  substance  containing  the  carboxyl- 

OH~ 
group. 

In  this  explanation  of  the  formation  of  acids,  the  existence  of 
an  intermediate  compound  containing  three  hydroxyl-groups  is 
assumed.  Such  substances  are  not  known,  but  the  assumption 
seems  by  no  means  improbable,  because  compounds  containing 

/OC2H5 

three  alkoxyl-groups  exist;  for  example,  CH3  •  C—  -OC2H5. 

\OC2H5 
They  are  called  ortho-esters  (149). 

The  acids  CnH2nO2  can  be  formed  by  the  action  of  carbon 
monoxide  on  metallic  alkoxides  under  the  influence  of  heat: 

CH3.ONa  +  CO  -  CH3.COONa. 

The  formation  of  an  addition-product  between  CH3-ONa  and  CO 
can  be  explained  by  the  assumption  that  the  alkoxide  first  decom- 
poses into  CH.3  and  ONa. 

It  is  mentioned  in  45  and  46  that  oxidation  converts  the  primary 
alcohols  into  acids  of  the  general  formula  CnH2nO2,  with  the  same 


80] 


ACIDS,  CnH2n02. 


107 


number  of  C-atoms  in  the  molecule. 
— CH2OH  is  oxidized  to  — COOH. 


In  this  reaction  the  group 


The  higher  primary  alcohols  can  also  be  transformed  into  the 
corresponding  acids  by  heating  them  with  soda-lime,  free  hydrogen 
being  evolved: 

Ci7H,6  •  CH,OH  +XaOH  - C17H35 . COONa  +2H2. 

Stearyl  alcohol  Sodium  stearate 

Other  methods  arc  described  in  98,  145,  164,  232,  and  233. 

The  presence  of  hydroxyl  in  the  carboxyl-group  is  proved  by 
the  action  of  the  chlorides  of  phosphorus,  which  replace  the  OH- 
group  by  Cl,  as  with  the  alcohols. 

In  each  molecule  of  the  acids  of  this  series  there  is  one  hydrogen 
atom  replaceable  by  metals.  Only  the  carboxyl-hydrogen  atom  is 
in  direct  union  with  oxygen,  and  its  special  position  suggests  that 
it  is  the  replaceable  atom.  The  truth  of  this  supposition  has  been 
proved  by  treating  silver  acetate,  C2H3O2Ag,  with  ethyl  iodide: 
ethyl  acetate  is  formed,  and  not  butyric  acid,  which  would  result 
if  the  Ag-atom  were  attached  to  the  methyl  C-atom;  thus, 
CH2Ag-COOH. 

80.  The  lower  members  of  this  series  of  acids  are  liquid  at 
ordinary  temperatures.  They  can  be  distilled  without  decomposi- 


-20- 


60 


•10        11        12 

->  NUMBER  OF  CARBON  ATOMS 


FIG.  30. — MELTING-POINT  CURVK  OF  THE  FATTY  ACIDS. 


tion,  and  have  a  very  irritating  and  strongly  acid  odour  in  the 
concentrated   state.     They   are   miscible   in   all   proportions  with 


108 


ORGANIC   CHEMISTRY. 


[§80 


water.  The  middle  members  (C4 — C9)  have  a  disagreeable  rancid 
smell.  They  are  of  an  oily  nature,  and  do  not  mix  with  water  in 
all  proportions.  The  higher  members,  beginning  at  CIQ,  are  solid  at 
ordinary  temperature,  without  odour,  and  resemble  paraffin-wax 
in  character.  They  are  almost  insoluble  in  water,  and  cannot 
be  distilled  at  the  atmospheric  pressure  without  decomposition. 
All  the  acids  of  this  series  dissolve  readily  in  alcohol  and 
ether.  Except  the  first  member,  they  are  very  stable  towards 
oxidizing  agents. 

The  acids  of  the  series  CnH2n02  are  called  fatty  acids,  some  of 
the  higher  members  having  been  first  obtained  from  fats. 

Many  of  the  fatty  acids  are  natural  products,  occurring  either 
m  the  free  state  or  as  esters,  and  are  of  great  theoretical  and  tech- 
nical importance.  The  table  contains  the  names,  formulae,  and 
certain  physical  constants  of  the  normal-chain  acids  of  the  series 
CnH2n02. 


Name 

Formula. 

Melting-point. 

Boiling-point. 

Specific  Gravity 

Formic  acid.  

CH2O2 

8-3° 

101° 

1-2310  (10°) 

Acetic  acid  
Propionic  acid  
Butyric  acid  

C2H4O2 
C3Hc02 
C4H8O2 

16-671°* 
-22° 
-  3-12° 

118° 

141° 
162° 

1-0532  (lb°) 
0-G985  (14°) 
0-9599  (19-1°) 

Valeric  acid  

-58-5° 

186° 

0-9560  (0°) 

Caproic  acid  

C6H12O2 

—   1-5° 

205° 

0-9450  (0°) 

Heptylic  acid  
Caprylic  acid  

C7H1402 

-10-5° 
16-5° 

223° 
237-5° 

0-9186  (17-2°) 
0-Q100  ?20°^ 

Nonylic  acid  
Capric  acid 

C9H1802 

12-5° 
31-4° 

254° 
269° 

0-9110  (M.P.) 

O.QOA        ?Q70\ 

Palmitic  acid 

C  H  Q2 

62-618° 

26Q°  t 

Margaric  acid 

60° 

277°  t 

Stearic  acid  

CisHseOu 

69-32° 

287°  f 

—  . 

*  At  760  mm. 


t  At  100  mm. 


Although  the  boiling-points  rise  with  increase  in  the  number 
of  C-atoms  in  the  molecule,  the  melting-points  of  the  acids  with  an 
even  number  of  C-atoms  are  higher  than  those  of  the  acids  imme- 
diately preceding  and  succeeding  them,  with  an  odd  number  of 
C-atoms  (Fig.  30).  This  phenomenon  has  also  been  observed  in 
some  other  homologous  series. 

The  residual  groups  which  would  result  by  elimination  of  hy- 
droxyl  from  fatty-acid  molecules  are  unknown  in  the  free  state, 
but  named  after  the  corresponding  acids  by  changing  the  termina- 
.ation  "ic  "  into  "yl";  thus, 


§  81]  FORMIC  ACID.  109 

H-CO  Formyl, 
CH3-CO  Acetyl, 
C2H5.CO   Propionyl, 
C3H7-CO  Butyryl, 
C4H9-CO  Valeryl, 
etc. 

Formic  Acid,  H-COOH. 

81.  Formic  acid  derives  its  name  from  its  presence  in  ants 
(Latin,  formica).  It  can  be  obtained  by  passing  carbon  monoxide 
over  soda-lime  at  210°,  the  yield  being  good  (79),  but  is  usually 
prepared  by  another  method  (153) .  It  can  also  be  obtained  by  oxi- 
dizing methyl  alcohol.  A  peculiar  method  of  synthesis  is  to  pass 
a  silent  electric  discharge  through  a  mixture  of  carbon  monoxide 
and  steam,  or  carbon  dioxide  and  hydrogen.  MOISSAN  discovered 
a  mode  of  synthesis  from  carbon  dioxide  and  potassium  hydride: 
KH  +  C02  =  H-COOK. 

Pure  formic  acid  is  a  colourless  liquid  of  irritating  odour.  Its 
salts  are  called  formates:  they  are  soluble  in  water,  some  only  with 
difficulty. 

Formic  acid  is  distinguished  from  its  homologues:  first,  by 
its  susceptibility  to  oxidation,  and  hence  its  reducing  power;  second, 
in  being  readily  decomposed  into  carbon  monoxide  and  water. 
When  mercuric  oxide  is  added  to  a  solution  of  formic  acid,a  solution 
of  mercuric  formate  is  obtained.  If  this  solution  be  filtered  and 
warmed,  mercurous  formate  is  precipitated  with  evolution  of  car- 
bon dioxide,  and  on  further  warming,  metallic  mercury  is  liberated: 
OOCH  H  COO 

Hg  IQQCH+HICOO!HS  =  2HgoocH+co2+HcooH; 

J ! '  Mercurous 

Mercuric  formate  formate 


Hg|OOCH  +  H|CQO|Hg  =  2Hg  +  C02  -f-HCOOH. 

Mercurous  formate 

In  this  process  half  of  the  formic  acid  in  the  salt  is  set  free,  and 
half  is  oxidized.  When  a  solution  of  silver  formate  is  warmed, 
an  exactly  analogous  reaction  takes  place;  metallic  silver  is  pre- 
cipitated, carbon  dioxide  evolved,  and  half  of  the  acid  liberated. 

When  formic  acid  is  warmed  with  concentrated  sulphuric  acid, 
water  and  carbon  monoxide  are  formed: 
[HjCOjOH|  =  H2 


110 


ORGANIC  CHEMISTRY. 


[§82 


The  introduction  of  finely  powdered  metallic  rhodium,  or  other 
metals  of  the  platinum  group,  into  an  aqueous  solution  of  the 
acid  effects  its  decomposition  into  carbon  dioxide  and  hydrogen, 
the  metal  acting  as  an  accelerating  catalyst. 

It  is  apparent  that  the  properties  of  formic  acid  differ  somewhat 
from  those  of  the  other  acids  of  the  homologous  series  in  which  it 
is  the  lowest  member.  A  similar  phenomenon  is  of  frequent 
occurrence. 

Acetic  Acid,  CH3.COOH. 

82.  Acetic  acid  has  been  known  longer  than  any  other  acid. 
It  is  manufactured  by  two  different  methods. 

a.  By  oxidation  of  dilute  alcohol,  wine,  beer,  etc.,  by  exposure 
to  the  air,  with  production  of  vinegar.  The  oxygen  of  the  atmos- 
phere acts  upon  the  alcohol  by  the  aid  of  bacteria,  and  the  process 
must  be  so  regulated  that  these  bacteria  produce  the  greatest  pos- 
sible effect.  To  this  end  it  is  important  that  the  temperature 
should  be  kept  between  20°  and  35°. 

In  the  "  quick "    or   German    process   for   the  preparation  of 

vinegar  (Fig.  31),  dilute  alcohol 
(6-10  per  cent.)  is  allowed  to  drop 
on  beech-wood  shavings  contained 
in  a  vat  with  a  perforated  false 
bottom,  a.  Holes  bored  in  the 
sides  of  the  vat  near  the  bottom 
serve  to  admit  an  ascending  stream 
of  air,  opposite  in  direction  to  that 
of  the  alcohol.  The  shavings  of 
beech-wood  distribute  the  liquid 
over  a  very  large  surface,  thus 
facilitating  the  oxidizing  action  of 
the  air,  while  at  the  same  time 
they  serve  as  a  feeding  ground  for 
the  bacteria. 

6.  Acetic  acid  is  obtained  in  the 


FIG.  SI.-PREPARATIONOF  VINE- 


GAR  BY  THE  "QUICK"  OR 
MAN  PROCESS. 


-  distillation  of  wood  (42). 


By  treat- 
e    acjj    is 

converted  into  calcium  acetate,  which  is  freed  from  tarry  im- 
purities by  heating  to  200°  in  the  air.  The  acetic  acid  is  then 
liberated  by  distilling  with  an  equivalent  quantity  of  concentrated. 


§  82]  ACETIC  ACID.  Ill 

hydrochloric  acid.     It  can  be  purified  by  distillation  from  potas- 
sium dichromate,  being  very  stable  towards  oxidizing  agents. 

At  temperatures  below  16-671°/760  mm.,  anhydrous  acetic 
acid  is  solid  and  has  much  the  appearance  of  ice;  hence  the 
name  glacial  acetic  acid.  The  solid  acid  has  a  penetrating  odour, 
and  is  obtained  by  allowing  a  very  concentrated  solution  of  acetic 
acid  to  solidify,  pouring  off  the  liquid  residue,  melting  the  solidified 
acid,  again  allowing  it  to  crystallize,  and  so  on,  these  operations 
being  repeated  until  the  melting-point  is  constant.  A  rise  of 
temperature  and  contraction  of  volume  occur  when  glacial  acetic 
acid  is  mixed  with  water,  the  maximum  rise  and  contraction  being 
produced  by  mixing  in  the  proportion  of  one  gramme-molecule 
of  acetic  acid  to  one  gramme-molecule  of  water.  This  fact 
indicates  the  existence  of  a  compound  called  ortho-acetic  acid 
(79),  with  the  formula  CH3-COOH.H2O=CH3.C(OH)3. 

The  existence  of  a  compound  of  the  formula,  C2H402,H20r  is  also 
indicated  by  other  physical  properties,  such  as  viscosity,  a  constant 
measured  by  determining  the  rate  of  efflux  of  a  known  volume  of 
the  liquid  through  a  capillary  tube  at  constant  temperature,  since 
changes  of  temperature  greatly  affect  its  value.  The  rate  of  efflux 
is  proportional  to  the  viscosity.  With  mixtures  of  acetic  acid  and 
water  the  viscosity  attains  a  fairly  distinct  maximum  for  the 
molecular  ratio  1:1.  In  a  number  of  other  instances  there  are 
breaks  corresponding  with  molecular  proportions  in  the  curves 
plotted  with  the  compositions  of  the  liquid  mixture  as  abscissae, 
and  the  viscosities  as  ordinates.  An  example  is  furnished  by 
mixtures  of  methyl  alcohol  and  water  corresponding  with  the 
formula,  CH3OH,2H20  and  CH3OH,3H20. 

A  fifty-five  per  cent,  solution  of  glacial  acetic  acid  in  water  has 
the  same  specific  gravity  as  the  pure,  anhydrous  acid.  When 
water  is  added  to  glacial  acetic  acid,  the  specific  gravity  of  the 
mixture  first  rises:  further  addition  of  water  causes  it  to  fall. 
This  circumstance  makes  it  impossible  to  determine  the  amount  of 
acid  present  in  such  mixtures  by  the  simple  use  of  the  hydrometer. 

The  strength  of  very  concentrated  acetic  acid  is  best  determined 
by  an  observation  of  its  melting-point,  a  thermometer  graduated 
in  tenths  of  a  degree  being  used.  In  accordance  with  the  formula 
given  in  12, 

AM  =  Constant, 


112  ORGANIC  CHEMISTRY.  [§  83 

the  presence  of  1  per  cent,  of  water  (molecular  weight  18)  would, 
since  the  constant  for  glacial  acetic  acid  is  39,  cause  a  depression 

39 
(A)  of  —    or  2 '16°.     Since  a  thermometer  graduated  in  tenths  can 

-lo 

easily  be  read  to  within  one-twentieth  of  a  degree,  the  amount  of 

1 
water  can  be  determined  to  within  — —    or  0-025  per  cent. 

2  •  lo  X2 

This  is  a  degree  of  accuracy  unattainable  by  titration. 

When  either  no  very  great  accuracy  is  required,  or  the  acetic 
acid  is  dilute,  it  is  best  to  determine  the  strength  by  titrating  a 
weighed  quantity  of  the  solution  with  a  standard  solution  of  alkali. 

The  vapour-density  of  acetic  acid  at  temperatures  slightly 
above  its  boiling-point  is  twice  as  great  as  that  corresponding 
with  the  formula  C2H4O2.  At  about  209°,  however,  the  vapour- 
density  is  normal.  A  similar  phenomenon  has  been  observed 
with  many  acids  of  this  series  and  other  substances  (288) . 

Absolutely  pure  acetic  acid  is  not  attacked  by  chlorine  or 
bromine  in  absence  of  light.  The  acid  can  be  prepared  in  this 
condition  by  distilling  from  phosphoric  acid  the  highly  concen- 
trated acid  melting  above  16°. 

83.  The  acetates,  or  salts  of  acetic  acid,  are  soluble  in  water, 
the  silver  salt  dissolving  with  difficulty.  When  ferric  chloride  is 
added  to  a  solution  of  an  acetate,  such  as  sodium  acetate,  a  blood- 
red  colour  is  produced,  owing  to  the  formation  of  a  complex 
acetoferric  acetate,  the  salts  of  formic  and  propionic  acids  react- 
ing similarly.  When  this  solution  is  sufficiently  dilute,  brown- 
red  basic  ferric  acetate,  Fe(OH)2C2H3O2,  is  precipitated  on  boil- 
ing, acetic  acid  being  simultaneously  liberated. 

The  dry  distillation  of  anhydrous  sodium  acetate  with  soda- 
lime  produces  methane : 

CH3  •  COONa  +  Na  OH  =  CH4  +  Na2C03. 

A  very  delicate  test  for  acetic  acid  is  the  formation  of  cacodyl 
oxide  (73).  Owing  to  the  extremely  poisonous  nature  of  this  sub- 
stance, great  care  must  be  exercised  in  applying  the  test.  Among 
the  acetates  of  technical  importance  are  lead  acetate  ("  sugar  of 
lead  "),  basic  lead  acetate,  and  aluminium  acetate.  The  first  two 
are  used  in  the  manufacture  of  white  lead,  and  the  third  as  a 
mordant  in  calico-printing  (340). 


§84]  BUTYRIC  ACIDS.  113 

Butyric  Acids,  C4H8O2. 

84.  Two  isomeric  acids  with  the  formula  C4H8O2  are  known. 
They  are  normal  butyric  acid,  CH3-CH2.CH2.COOH,  and  isobuty- 

prr 

ric  acid,  ^3>CH.COOH.     The  constitution  of  these  acids  is 

proved  by  their  synthesis,  the  normal  compound  being  obtained 
from  n-propyl  iodide,  and  the  iso-acid  from  rsopropyl  iodide: 

CH3.CH2.CH2I  ->CH3.CH2.CH2.CN  ->CH3.CH2.CH2.COOH. 
!**3  >  CHI  ->  p^3  >  CH  •  CN  -»  p^3  >  CH  •  COOH. 

V^-tl3  ^-ti3  v^n-3 

The  normal  compound  is  also  called  "fermentation"  butyric 
acid,  from  the  fact  that  it  can  be  obtained  by  the  fermentation 
un^er  certain  conditions  of  such  substances  as  sugar.  It  has  an 
extremely  disagreeable  odour,  and  can  only  be  oxidized  with  diffi- 
culty. 

Butter  contains  about  2-3  per  cent,  of  n-butyric  acid,  along  with 
smaller  quantities  of  other  volatile  acids  of  the  fatty  series,  such  as 
caproic  acid:  they  are  probably  present  as  esters.  Since  volatile 
fatty  acids  are  not  obtained  by  saponification  of  other  fats,  whether 
animal  or  vegetable,  their  presence  furnishes  the  most  characteristic 
distinction  between  butter  and  margarine:  the  latter  is  a  mixture  of 
animal  and  vegetable  fats.  Since  the  percentage  of  volatile  fatty 
Acids  in  butter  is  not  a  constant  quantity,  but  may  vary  between 
wide  limits,  it  is  not  always  possible  to  determine  that  a  sample  of 
butter  has  been  adulterated  with  margarine  by  estimating  these 
acids.  By  the  application  of  other  tests,  however,  it  is  sometimes 
possible  to  decide  in  such  doubtful  cases. 

isoButyric  acid  also  has  a  very  disagreeable  odour.  It  contains 
a  tertiary  carbon  atom,  and  since  such  compounds  are  readily 
oxidized,  oxidation  affords  a  method  of  distinguishing  between  the 
normal  acid  and  the  t'so-acid. 

The  calcium  salts  of  these  acids  also  exhibit  a  remarkable  dif- 
ference, that  of  the  normal  acid  being  less  soluble  in  hot  water 
than  in  cold,  while  that  of  the  iso-acid  follows  the  ordinary  rule, 
and  is  more  soluble  in  hot  than  in  cold  water.  When  heated  to 
about  80°,  a  solution  of  normal  calcium  butyrate  saturated  at  0° 
deposits  considerable  quantities  of  the  salt. 


114  ORGANIC  CHEMISTRY.  [§85 

In  accordance  with  the  principle  of  mobile  equilibrium  ("  In- 
organic Chemistry,"  235),  calcium  n-butyrate  should  dissolve  in 
water  with  slight  evolution  of  heat,  and  calcium  isobutyrate  with 
slight  absorption  of  heat.  This  view  is  fully  supported  by  the 
results  of  experiment. 

Higher  Fatty  Acids,  CnH2nO2. 

85.  Many  of  the  higher  members  of  the  series  of  fatty  acids  are 
natural  products,  chief  among  them  being  palmitic  acid,  C16H32O2, 
and  stco,ric  acid,  C18H36O2,  both  with  normal  carbon  chains  (137). 
In  the  form  of  esters  of  glycerol  (154),  these  two  acids  occur  in 
large  quantities  as  the  principal  constituent  of  most  animal  and 
vegetable  fats,  from  which  they  are  obtained  by  saponification,  a 
process  carried  out  by  heating  either  with  slaked  lime  (95),  or 
with  concentrated  sulphuric  acid.  The  latter  causes  slight  car- 
bonization, imparting  a  dark  colour  to  the  fatty  acids.  They  can. 
be  purified  by  distillation  with  superheated  steam. 

Another  method  of  decomposing  the  fats  into  glycerol  and  a 
fatty  acid  depends  upon  the  action  of  an  enzyme  (222)  present  in 
castor-seed  (Latin,  ricinus  communis).  After  removal  of  the  oil,  the 
powdered  seeds  are  intimately  mixed  with  the  fat:  on  addition  of 
a  dilute  acid,  such  as  decinormal  sulphuric  acid,  an  emulsion  is 
formed.  If  the  mixture  is  kept  at  a  temperature  of  30°-40°  for 
two  or  three  days,  the  fatty  acids  are  set  free  in  a  very  pure  state; 
on  gentle  heating,  the  emulsion  then  separates  into  two  layers,  the 
upper  consisting  of  the  free  acids,  and  the  lower  of  an  aqueous  solu- 
tion containing  40-50  per  cent,  of  glycerol. 

Saponification  of  fats  yields  a  mixture  of  acids,  semi-solid  at 
ordinary  temperatures.  This  mixture  contains  the  two  acids  men- 
tioned above,  melting  at  62°  and  69°  respectively,  when  pure;  but 
when  mixed,  each  lowers  the  melting-point  of  the  other  (25).  More- 
over, liquid  oleic  acid,  belonging  to  another  homologous  series,  is 
also  present:  it  can  be  pressed  out  of  the  mixture,  leaving  a  white, 
solid  substance  used  in  the  manufacture  of  "stearine"  candles. 
For  this  purpose  the  "stearine"  is  melted,  and  after  addition  of  a 
small  proportion  of  paraffin-wax,  to  prevent  crystallization  of  the 
fatty  acids,  which  would  make  the  candles  brittle,  the  molten  sub- 
stance is  poured  into  moulds,  in  the  axes  of  which  wicks  are  fas- 
tened. 


§  86]  SOAP.  115 

Soaps  consist  chiefly  of  the  alkali-metal  salts  of  the  acids  con- 
tained in  fats.  They  are  prepared  by  saponifying  fats  with  a 
solution  of  caustic  soda  or  of  caustic  potash  heated  to  the  boiling- 
temperature.  Potassium-soap  is  called  "soft  soap,"  and  is  usually 
yellow.  In  some  countries  it  is  tinted  green  by  the  addition  of  in- 
digo, and  is  then  known  as  " green  soap."  Potassium-soap  contains 
not  only  the  potassium  salts  of  the  acids,  but  also  the  glycerol  pro- 
duced in  the  reaction,  and  a  considerable  proportion  of  water. 
Sodium-soap  is  hard:  it  is  separated  from  the  reaction-mixture, 
after  sapomfication  is  complete,  by  "salting-out,"  which  consists 
in  the  addition  of  solid  common  salt  to  the  mixture  at  thj  boiling- 
temperature.  Since  the  sodium  salts  of  the  acids  are  insoluble  in 
a  concentrated  solution  of  sodium  chloride,  the  soap  separates  out 
in  the  molten  state,  forming  a  layer  on  the  surface  of  the  brine, 
in  which  the  glycerol  remains  dissolved.  The  soap  thus  obtained 
consists  of  the  sodium  salts  of  the  acids,  with  a  small  percentage  of 
water. 

86.  The  cleansing  action  of  soap  may  be  explained  as  follows. 
When  an  alkali-metal  salt  of  one  of  the  higher  fatty  acids  is  brought 
into  contact  with  a  large  excess  of  water,  it  decomposes  with  for- 
mation of  free  alkali,  a  fact  that  was  pointed  out  by  CHEVREUL  as 
early  as  at  the  beginning  of  the  nineteenth  century.  The  acid  thus 
liberated  unites  with  a  second  molecule  of  the  salt  to  form  an  in- 
soluble substance,  which  with  the  water  produces  the  lather.  The 
presence  of  free  alkali  in  dilute  soap-solutions  can  be  experimentally 
demonstrated.  A  concentrated  soap-solution  is  only  very  slightly 
coloured  by  phenolphthalein;  but  the  addition  of  a  large  propor- 
tion of  water  causes  the  development  of  the  red  colour,  due  to 
the  action  of  the  base  thus  liberated  on  the  phenolphthalein.  The 
soap  has  therefore  undergone  hydrolytic  dissociation,  owing  to  the 
weak  acidic  character  of  the  higher  fatty  acids. 

The  soiling  of  the  skin,  clothes,  and  so  on,  is  partly  due  to 
substances  of  a  fatty  nature,  and  partly  to  soot,  iron  oxide,  or 
clay.  An  insight  into  the  mechanism  of  the  removal  of  the 
fatty  substances  is  afforded  by  the  following  experiment.  When 
a  drop  of  oil  or  a  small  piece  of  fat  is  placed  in  water,  the  two 
substances  do  not  mix.  On  addition  of  a  few  drops  of  caustic- 
alkali  solution  to  the  water,  followed  by  vigorous  agitation  of 
the  mixture,  the  liquid  develops  a  milk-like  appearance,  due  to 


116  ORGANIC  CHEMISTRY.  [§87 

the  formation  of  an  emulsion  ("  Inorganic  Chemistry/'  196) 
consisting  of  minute  droplets  of  fat  suspended  in  the  liquid,  just 
as  in  milk.  The  alkali  liberated  from  the  soap  has  a  similar 
emulsifying  effect  on  the  dirt.  The  proportion  of  alkali  set  free 
from  soap  is  small  with  a  small  quantity  of  water,  larger  with  a 
large-  quantity;  but  the  addition  of  a  great  quantity  of  water 
produces  no  considerable  modification  of  the  concentration — the 
amount  of  free  alkali  in  unit  volume  of  the  liquid — since,  although 
it  produces  more  free  alkali,  it  simultaneously  dilutes  it.  The 
use  of  soap  has,  therefore,  the  effect  of  automatically  maintain- 
ing a  small  concentration  of  free  alkali  in  the  water.  There 
would  be  no  such  adjustment  if  free  alkali  were  employed  instead 
of  soap. 

Soot*  iron  oxide,  and  other  forms  of  dirt  adhere  very  tena- 
ciously to  the  skin  and  to  textiles,  and  either  cannot  be  removed 
by  rubbing  with  water  alone,  or  only  with  great  difficulty,  but 
the  cleansing  is  readily  effected  by  the  action  of  a  soap-solution. 
Its  action  must  be  ascribed  to  adsorption  of  the  dirt  by  the  acid 
alkali-metal  salts  of  the  fatty  acids,  the  product  formed  no  longer 
adhering  to  the  skin  or  fabric.  An  illustrative  experiment  is 
described  in  "  Laboratory  Manual/'  IX.,  16. 

Water  containing  a  certain  percentage  of  calcium  salts  is  called 
a  "hard"  water  (" Inorganic  Chemistry/'  259).  Such  water 
does  not  immediately  lather  with  soap,  but  causes  the  formation  of 
a  white,  flocculent  substance,  consisting  of  insoluble  calcium  salts 
of  the  fatty  acids.  Hard  water  is  therefore  unsuitable  for  washing, 
because  it  prevents  the  formation  of  a  lather,  and  also  because  the 
alkali  is  neutralized  and  thus  withdrawn  by  the  acid-radical  of 

the  calcium  salts  (sulphate  and  carbonate)  present. 
«» 

Electrolytic  Dissociation. 

87.  Molecules  of  acids,  bases,  and  salts  are  assumed  to  be  re- 
solved, on  solution  in  water,  into  ions,  charged  with  opposite  kinds 
of  electricity  ("Inorganic  Chemistry,"  65  and  66).  In  such  a  solu- 
tion, an  acid  is  partially  or  completely  dissociated  into  positively 
charged  hydrogen  ions,  H*  (cations),  and  negatively  charged 
anions:  for  example,  acetic  acid  is  resolved  into  H*  (positive),  and 
(C2H3O2)'  (negative).  Bases  yield  a  positively  charged  metallic: 


87] 


ELECTROLYTIC  DISSOCIATION. 


117 


ion,  and  a  negatively  charged  OH'-ion;   salts  a  positively  charged 
metallic  ion,  and  a  negatively  charged  acid-radical  ion. 

It  is  further  stated  (Ibid.,  66)  that  in  the  solution  of  a  partly 
ionized  substance  there  is  an  equilibrium  which  for  a  monobasic 
.acid  can  be  expressed  by 


where  Z'  represents  the  acid-radicaL     If  v  is  the  volume  in  litres 
containing  one  gramme-molecule  of  the  acid,  and  a  is  the  portion 


ionized,  then  the  concentration  of  the  ions  is  —  ,  and  that  of  the 
1 


non-ionized  portion  is 


a 


The  equation  representing  the  equi- 


librium in  the  above  example  of  a  monobasic  acid  is,  therefore 

(Ibid.,  49), 

,1-a     /a\2  a2         . 

I* —  I  r\i*     — —  u* 

n/ I     •     vl          / .-  — A/» 

v        \v  J  v(l  —  a) 

In  this  equation  k  is  constant,  and  is  called  the  ionization-constant. 
It  has  been  proved  that  this  equation  affords  an  exact  measure  of 
the  amount  of  ionization  for  the  very  weak  organic  acids;  that  is, 
expresses  accurately  the  connection  between  the  dilution  v  and 
the  ionization  a.  For  this  reason  it  is  called  the  law  of  dilution. 
It  was  discovered  by  OSTWALD,  who  dissolved  one  gramme-molecule 
of  an  acid  in  different  quantities  of  water,  v,  and  ascertained  the 
ionizations  a  by  determining  the  electric  conductivity.  On  sub- 
stituting the  values  obtained  for  a  and  v  respectively  in  the  expres- 

a2 
sion  -        — ,  the  latter  was  always  found  to  have  the  same  value, 


.as  it  must  if  k  is  constant. 

The  accuracy  of  this  law  is  evident  from  the  examples  in  the 
following  table. 


Acetic  Acid. 

Propionic  Acid. 

n-Butyric  Acid. 

v 

lOOa 

10<jfc 

v 

lOOa 

10"A; 

v 

lOOa 

10"A: 

8 

1-193 

0-180 

8 

1-016 

0-130 

8 

1-068 

0-144 

16 

1-673 

0-179 

16 

1-452 

0-134 

16 

1-536 

0-150 

32 

2-380 

0-182 

32 

2-050 

0-134 

32 

2-165 

0-149 

64 

3-33 

0-179 

64 

2-895 

0-135 

64 

3-053 

0-150 

128 

4-68 

0-179 

128 

4-04 

0-133 

128 

4-292 

0-150 

1024 

12-66 

0-177 

1024 

10-79 

0-128 

1024 

11-41 

0-144 

118  ORGANIC  CHEMISTRY.  [§  88 

88.  The  "  strength"  of  acids  depends  upon  their  degree  of 
ionization,  strong  acids  undergoing  considerable,  and  weak  acids 
but  slight,  ionization.  Since  the  constant  k  rises  or  falls  in  value 
simultaneously  with  a,  and  is  independent  of  the  concentration, 
it  affords  a  convenient  measure  of  the  strength  of  an  acid. 

The  table  shows  the  values  of  104&  for  certain  fatty  acids. 

Formic       ...  Acetic  Propionic         n-Butyric          Valeric 

2-14,  0-18,  0-13,  0-15,  0-16. 

It  is  noteworthy  that  formic  acid  has  a  greater  ionizat ion-constant, 
and  is  therefore  stronger,  than  its  homologues,  another  example  of 
the  difference  between  it  and  the  other  members  of  the  series. 

A  comparison  of  these  acids  with  such  strong  mineral  acids  as 
sulphuric  acid  and  hydrochloric  acid,  from  the  point  of  view  of  the 
magnitude  of  their  ionization-constants,  shows  that  the  former  are 
very  much  weaker  than  the  latter.  When  v=I6,  then  for  hydro- 
chloric acid  100a  =  95'55,  and  for  acetic  acid  only  1-673.  It  is 
obvious  that  100  a  is  the  amount  ionized,  expressed  in  percentage, 

The  weak  organic  acids  follow  the  law  of  dilution  :  the  strong 
mineral  acids  do  not.  No  perfectly  satisfactory  explanation  of  this 
phenomenon  has  been  suggested  hitherto. 


DERIVATIVES  OF  THE  FATTY  ACIDS  OBTAINED  BY 
MODIFYING   THE   CARBOXYL-GROUP. 

89.  The  carboxyl-group  may  be  modified  by  the  exchange  of 
its  oxygen  atoms  or  hydroxyl-group  for  other  elements  or  groups. 
The  compounds  described  in  this  chapter  contain  such  modified 
carboxyl-groups. 

I.  Acid  Chlorides. 

Acid  chlorides  are  derived  from  acids  by  replacement  of  the 
hydroxyl-group  by  chlorine,  and  consequently  contain  the  group 
—  COC1.  They  are  obtained  from  the  acids  by  the  action  of  the 
chlorides  of  phosphorus,  PCI  5  and  PC13,  or  of  phosphorus  oxy- 
chloride,  POC13: 


3CnH2n+1.COOH  +  2PCl3  =  3CnH2n+1.COCl+P2O3 

The  ease  with  which  the  acid  chlorides  are  converted  into  the  cor- 
responding acids  is  a  proof  that  the  chlorine  atom  has  replaced 
the  hydroxyl-group.  For  the  lower  members  this  conversion  is 
effected  by  merely  bringing  them  into  contact  with  water.  If  the 
chlorine  atom  had  substituted  hydrogen  of  the  alkyl-group,  there 
would  be  no  reaction,  since  an  alkyl  chloride  is  not  decomposed  by 
water  at  ordinary  temperatures. 

The  acid  chlorides  of  this  series,  at  least  the  lower  members, 
are  liquid,  and  have  a  suffocating,  irritating  odour.  The  chloride 
corresponding  to  formic  acid  is  not  known.  Acetyl  chloride, 
CH3COC1,  fumes  in  the  air,  and  can  be  distilled  without  decom- 
position. It  boils  at  55°,  and  its  specific  gravity  is  1-13  at  0°. 

Acetyl  chloride  is  employed  in  detecting  the  presence  of  hy- 
droxyl  in  organic  compounds.  Hydroxyl  is  replaced  by  acetyl: 
thus,  alcohols  form  esters  of  acetic  acid: 

tt]OC.CH3  =  RO-OC-CHa+HCI. 

119 


120  ORGANIC  CHEMISTRY.  [§§  90,  91 

The  compound  to  be  tested  is  allowed  to  remain  for  some  time  in 
contact  with  acetyl  chloride,  either  at  the  ordinary  temperature  or 
with  gentle  warming.  To  ascertain  whether  an  acetyl-compound 
has  been  formed,  the  purified  product  is  analyzed  or  saponified. 
If  saponification  yields  acetic  acid,  an  acetyl-derivative  was  present. 
The  homologues  of  acetyl  chloride  are  also  sometimes  employed 
in  the  detection  of  hyclroxyl-groups. 

The  acid  chlorides  also  react  with  the  mercaptans,  forming  sul> 
stances  of  the  type  of  acetyl-compounds. 

II.  Acid  Anhydrides. 

90.  Acid  anhydrides  are  formed  by  interaction  of  the  alkali- 
metal  salts  of  acids  and  acid  chlorides: 


CH3-CO|Cl  +  Na|O.OC.CH3  = 

Acetic  anhydride 

Higher  anhydrides  are  best  obtained  by  heating  the  sodium  salts 
of  the  higher  acids  with  acetic  anhydride. 

The  acid  chlorides  may  be  regarded  as  mixed  anhydrides  of 
hydrochloric  acid  and  an  acid,  a  view  supported  by  their  formation 
from  thess  two  acids  by  treatment  with  phosphorus  pentoxide  as  a 
dehydrating  agent. 

Mixed  anhydrides  of  the  fatty  acids  themselves  exist,  although 
when  distilled  they  decompose  into  the  anhydrides  of  the  two  acids. 

The  lower  members  of  this  series  are  liquids,  and  have  a  dis- 
agreeable, suffocating  odour.  Acetic  anhydride  has  a  specific 
gravity  D420  =  1-0820  and^boils  at  139-53/760  mm.  At  ordinary 
temperatures  it  is  soluble  in  about  ten  times  its  volume  of  water, 
the  solution  decomposing  slowly  with  formation  of  acetic  acid. 
In  this  respect  it  differs  from  acetyl  chloride,  which  reacts  momen- 
tarily and  vigorously  with  water,  yielding  acetic  acid  and  hydro- 
chloric acid.  Like  acetyl  chloride  it  is  used  in  testing  for  the 
presence  of  the  hydroxyl-group.  No  anhydride  of  formic  acid 
is  known. 

III.  Esters. 

91.  Esters  result  from  the  interaction  of  acid  chlorides,  or 
anhydrides,  and  alcohols: 

CH3-  CO|CTTH|OC2H5  =CH3'  COOC2H5  +  HC1. 


§  91]  ESTERS.  121 

They  are  also  formed  by  direct  treatment  of  the  alcohol  with  th* 
acid,  although  extremely  slowly  at  ordinary  temperatures: 

CH3.COOH  +  HOC2H6  -  CH3.COOC2H5+H2O. 

The  velocity  of  the  reaction  is  much  increased  by  a  rise  of  tem- 
perature. Esters  are  also  obtained  by  the  action  of  the  silver  salt 
of  an  acid  upon  an  alkyl  iodide. 

The  following  is  a  characteristic  method  frequently  used  for 
the  preparation  of  these  compounds.  Dry  hydrochloric-acid  gas 
is  passed  through  a  mixture  of  absolute  alcohol  and  the  anhydrous 
organic  acid.  After  some  time  the  reaction-mixture  is  poured  into 
water,  whereupon  the  ester  separates  out,  owing  to  its  slight  solu- 
bility. The  formation  of  esters  in  this  manner  may  be  explained 
on  the  assumption  that  a  very  small  quantity  of  the  hydrochloric 
acid  unites  with  the  organic  acid,  water  being  eliminated,  and  a 
minute  quantity  of  the  acid  chloride  formed: 

CH3.COOH  +  HC1  =  CH3.COC1  +  H2O. 

It  is  true  that  for  each  molecule  of  acid  chloride  formed  in  accord- 
ance with  this  equation  an  equivalent  quantity  of  water  is  pro- 
duced, sufficient  to  reconvert  the  chloride  into  the  acid  and  hydro- 
chloric acid.  There  is,  however,  such  an  infinitely  greater  number 
of  molecules  of  alcohol  tl>an  of  water  with  which  the  chloride  can 
react,  that  the  probability  of  the  formation  of  an  ester  is  very 
much  greater  than  the  probability  of  the  regeneration  of  the  acid. 
The  preponderance  continues  so  long  as  the  proportion  of  alcohol 
present  greatly  exceeds  that  of  the  water  formed;  so  that  when 
the  object  is  to  obtain  the  maximum  yield  of  ester,  the  organic  acid 
should  be  dissolved  in  a  large  excess  of  alcohol.  The  formation  of 
esters  is  called  estenfication. 

The  esters  are  colourless  liquids  of  neutral  reaction,  and  do  not 
mix  with  water  in  all  proportions.  They  are  lighter  than  water, 
most  of  them  having  a  specific  gravity  between  0-8  and  0-9. 
Many  of  them  are  characterized  by  their  agreeable  odour,  resem- 
bling that  of  fruits,  a  property  which  finds  practical  application  in 
their  employment  in  the  manufacture  of  artificial  fruit-essences. 
For  example,  isoamyl  isovalerate  (b.p.  196°)  has  an  odour  of 
apples,  ethyl  butyrate  (b.p.  121°)  of  pineapples,  isoamyl  acetate 
(b.p.  148°)  of  pears,  and  so  on. 


122  ORGANIC  CHEMISTRY.  [§  92 

Beeswax   is   a   natural   ester,    consisting   chiefly   of   melissyl 
palmitate,  C15H31-COOC3oH61. 

Tertiary  alcohols  can  be  synthesized  from  the  esters  by  means 
of  GRIGNARD'S  alkyl  magnesium  halides  (75)  : 

xOMgBr 

R.C^Xr  H  +R'MgBr  =  R.(^-OC2H6  . 
v  uu2±i5  \  g/ 

Addition-product 

The  addition-product  thus  obtained  reacts  with  a  second  molecule 
of  the  alkyl  magnesium  halide  . 

OMgBr  /OMgBr 

5  +  R"MgBr  =  R.C^R"       +C2 


On  decomposition  with  water  the  tertiary  alcohol  is  formed: 

/OMgBr  XOH 

R.C(-R"        +  H20  =  R  .(£-  R"  +  MgBrOH. 
\R'  \R' 

R,  R',  and  R"  represent  alkyl-groups 

92.  The  formation  of  esters  has  been  carefully  investigated  by 
several  chemists,  first  of  whom  were  BERTHELOT  and  PEAN  DE 
ST.  GILLES.  Their  researches  have  shown  that  the  reaction 
between  the  acid  and  the  alcohol  is  never  complete,  some  of  both 
remaining  uncombined  no  matter  how  long  the  process  has  been 
carried  on.  With  equivalent  quantities  of  acetic  acid  and  ethyl 
alcohol,  for  example,  the  final  product  is  such  that  from  each 
gramme-molecule  of  alcohol  and  acid  used,  only  two-thirds  of  a 
gramme-molecule  of  an  ester  and  cf  water  are  formed,  while  cne- 
third  of  a  gramme-molecule  of  the  alcohol  and  of  the  acid  respect- 
ively remain  uncombined.  The  same  limit  is  reached  when  equi- 
valent quantities  of  an  ester  and  water  are  brought  into  contact. 
An  equilibrium  between  the  four  substances,  alcohol,  acid,  ester, 
and  water,  is  ultimately  reached,  and  is  due  to  the  reversibility  of 
the  reaction  ("Inorganic  Chemistry,"  49).  It  may  be  represented 
as  follows  : 


§  93]  ESTERS.  123 

The  equation  of  equilibrium  deduced  in  Ibid.,  49-51,   may 
be  applied  to  the  formation  and  decomposition  of  esters.     It  is 

k(p-x)(q-x)  =k'x2,     or     (p-x)(q-x)  =Kx2, 

where  p  is  the  initial  concentration  of  the  alcohol  and  q  that  of  the 
acid,  while  x  represents  the  quantities  of  water  and  of  ester  re- 
spectively present  when  the  equilibrium  is  attained.  All  these  are 
expressed  in  gramme-molecules,  and  K  is  a  constant.  There  are 
here  two  opposing  reactions  taking  place  simultaneously,  so  that 
all  the  statements  referred  to  above  (loc.  cit.)  are  applicable  to  the 
present  instance.  Given  p,  q,  and  K,  the  unknown  quantity  x 
can  be  calculated. 

Numerous  observations  have  proved  that  K  is  equal  to  0  •  25  for 
the  system  ethyl  alcohol  +  acetic  acid.  When  one  gramme-molecule 
of  alcohol  (46  g.)  and  one  gramme-molecule  of  acetic  acid  (60  g.) 
are  brought  into  contact,  both  p  and  q  are  equal  to  1,  and  the  equa- 
tion is 


or     z-fz  +  £=, 

so  that 

*  =  f. 

It  follows  that  this  system  in  equilibrium  contains  $  gramme-molecule 
alcohol  +  5  gramme-molecule  acetic  ocid+f  gramme-molecule  water  + 
f  gramme-molecule  ester. 

93.  Several  deductions  can  be  drawn  from  the  equation 


These  deductions  had  been  established  by  experiment  long  before 
the  development  of  the  theory. 

1.  The  esterification  is  approximately  quantitative  only  when 
either  the  acid  or  the  alcohol  is  largely  in  excess. 

Putting  the  equation  in  the  form 

p-x  _        x 

--    lY  -  , 

x  q  —  x 

it  is  evident  that  when  the  quantity  of  alcohol  (p}  is  infinitely 
great,  the  left-hand  side  =  oo  .  This  is  true  of  the  right-hand  side 
when  q  =  x,  that  is,  when  all  the  acid  has  been  converted  into  ester. 


124  ORGANIC  CHEMISTRY.  [§  93 

It  also  holds  when  the  ratio  of  the  quantity  of  acid  to  alcohol  is 
infinitely  great,  the  whole  of  the  alcohol  changing  into  ester. 

Although  these  considerations  indicate  that  esterification  can  be 
complete  only  in  presence  of  an  infinitely  great  excess  cf  acid  or 
alcohol,  in  practice  the  very  nearly  theoretical  yield  of  ester  is 
obtained  when  the  ratio  of  the  quantity  of  acid  to  alcohol,  or  of 
alcohol  to  acid,  is  finite.  AJ  can  be  readily  deduced  from  the  equa- 
tion, this  holds  for  the  formation  of  ethyl  acetate  when  one  gramme- 
molecule  of  acid  reacts  with  ten  gramme-molecules  of  alcohol,  or, 
inversely,  when  one  gramme-molecule  of  alcohol  reacts  with  ten 
gramme-molecules  of  acid. 

2.  The  alcohol  and  the  acid  exercise  the  same  influence  on  the 
formation  of  esters:  thus,  if  a  mixture  containing  a  certain  num- 
ber of  acid  molecules  is  prepared  and  n  times  as  many  alcohol 
molecules,  and  another  with  the  proportions  of  acid  and  alcohol 
reversed,  then  the  number  of  molecules  of  acid  converted  into 
ester  in  the  first  mixture  is  equal  to  that  of  the  molecules  of  alcohol 
converted  in  the  second. 

When  p  gramme-molecules  of  alcohol  are  mixed  with  np 
gramme-molecules  of  acid,  the  equation  becomes 


x  np  —  x 

Inversely,  when  np  gramme-molecules  of  alcohol  are  added  to  p 
gramme-molecules  of  acid,  we  have 

np—x      T     x 
-  =  A  -  . 

x  p  —  x 

These  two  equations  are  identical. 

3.  The  addition  of  a  quantity  of  the  ester  to  the  mixture  of  the 
alcohol  and  the  acid  at  the  beginning  of  the  experiment  has  the 
same  effect  on  the  formation  of  ester  as  would  be  exerted  by  an 
equivalent  quantity  of  water. 

When  r  gramme-molecules  of  water  or  of  ester  are  added  to  a 
mixture  containing  p  gramme-molecules  of  alcohol  and  q  gramme- 
molecules  of  acid,  then  for  both  the  equation  becomes 


(p-x)(q-x)  =  K 
It  follows    that  the    equilibrium  is    influenced  to  the  same  ex- 


§§  94, 95]  ESTERS.  125 

tent  by  the  addition  of  equivalent  quantities  of  water  or  of 
ester. 

94.  A  typical  application  of  the  principle  of  mobile  equilibrium 
("Inorganic  Chemistry,"  235)  may  be  made  to  the  formation  of 
esters.     Although  the  velocities  of  formation  and  decomposition 
of  esters  depend  greatly  upon  the  temperature,  a  change  in  the 
latter   has  very  small   effect  upon  the  equilibrium.      At  10°  the 
limit  of  esterification   is   65 •  2  per  cent.;    at  220°  it  is  66-5  per 
cent.     In  accordance  with  the  principle  of   mobile    equilibrium, 
this  necessitates  that  the  heat  of  formation  of  the  ester  should 
be  very  small.     That  it  actually  is  so  has  been  established  by 
experiment. 

In  the  esterification  of  primary,  secondary,  and  tertiary  alcohols 
with  trichloroacetic  acid,  CC13  •COOH,  MICHAEL  proved  the  velocity- 
constant  k  to  have  a  much  higher  value  for  primary  alcohols  than 
for  secondary  and  tertiary.  For  n-propyl  alcohol  &Xl05=725, 
for  isopropyl  alcohol  98.  For  secondary  and  tertiary  alcohols  the 
value  of  the  constant  is  of  the  same  order;  for  secondary  butyl 
alcohol,  CH3-CHOH.C2H5,  fcX!05=90,  for  trimethylcarbinol, 
(CH3)3OOH,  118.  For  methyl  alcohol  the  constant  has  a  much 
higher  value  than  for  other  primary  alcohols,  since  &Xl05=3690. 
All  these  determinations  were  made  at  a  temperature  of  25°. 

95.  The  conversion  of  an  ester  into  an  acid  and  an  alcohol  by 
a  mineral  acid  or  an  alkali  is  called  saponification,  from  analogy 
to  the  formation  of  soap  from  alkali  and  fat  (85) .     It  is  represented 
by  an  equation  of  the  type 

CH3  -  COOC2H5  +  H2O  -  CH3  •  COOH  +  C2H5OH. 

The  action  of  the  mineral  acid  is  therefore  catalytic.  Its  presence 
only  accelerates  the  saponification:  the  same  result  would  be 
attained  without  it,  though  the  time  required  would  be  incom- 
parably longer  (81) .  If  the  concentration  of  the  ester  be  Ci,  that  of 
the  water  is  C2,  and  x  the  quantity  of  ester  saponified  during  the 

dx 

time  t,  then  the  velocity  of  saponification  £  =  -jr  f°r  each  mo- 
ment can  be  represented  by  the  equation  for  bimolecular  reac- 
tions ("  Inorganic  Chemistry,"  50): 

z)  ......     (1) 


126  ORGANIC  CHEMISTRY.  [§  95 

If  the  ester  is  dissolved  in  a  very  large  proportion  of  water,  the 
concentration  €2  of  the  water  is  only  very  slightly  altered  by  the 
saponification,  so  that  it  may  be  included  in  the  constant.  The 
equation  is  therefore  simplified  to  that  for  a  unimolecular  reaction  : 


(2) 


The  saponification  of  esters  by  bases  can  be  represented  by  an 
equation  of  the  type 

CH3.COOC2H5  +  NaOH  =  CH3.COONa  +  C2H 


It  is  a  bimolecular  reaction,  and  consequently  equation  (1)  is 
applicable  to  it. 

The  velocity  of  saponification  of  esters  by  acids  depends  largely 
upon  the  acid,  being  greater  the  stronger  the  acid  used.  It  has  been 
proved  that  the  velocity  of  saponification  depends  upon  the 
extent  of  electrolytic  dissociation  of  the  acid  employed.  From 
this  fact  it  may  be  concluded  that  the  saponifying  action  is  due 
to  the  hydrogen  ion  common  to  all  acids.  The  velocity  with  bases 
is  much  greater  than  with  acids;  thus,  for  dilute  (decinormal)  solu- 
tions of  caustic  potash  and  hydrochloric  acid,  the  ratio  of  the 
velocity-constants  K  for  the  saponification  of  methyl  acetate  is 
1350:  1.  The  velocity  of  saponification  by  bases  also  depends  upon 
their  electrolytic  dissociation.  Ammonium  hydroxide,  for  example, 
being  considerably  less  ionized  than  caustic  potash  or  caustic  soda, 
saponifies  much  more  slowly  than  either  of  these  bases.  Saponifi- 
cation is  therefore  caused  by  the  hydroxyl-ion  common  to  all 
bases. 

The  velocity  of  ester-saponification,  being  proportional  to  the 
concentration  of  the  hydrogen  ions  or  hydroxyl-ions,  can  be  em- 
ployed in  determining  this  concentration.  By  its  aid,  the  degree 
of  hydrolytic  dissociation  of  potassium  cyanide,  carbonates  of 
alkali-metals,  and  other  salts  can  be  ascertained,  and  also  the 
hydrogen-ionization  of  acid  salts,  such  as  potassium  hydrogen  sul- 
phate, KHSO4. 

In  the  technical  saponification  of  fats  with  slaked  lime  (85)  a 
much  smaller  amount  of  this  base  is  used  than  would  be  needed  to 
neutralize  all  the  acid  obtained:  the  saponification  is  nevertheless 
complete.  This  is  due  to  the  fact  that  the  higher  fatty  acids  are 


§  96]  THIO-ACIDS  AND  ACID  AMIDES.  127 

very  weak,  so  that  their  salts  undergo  partial  hydrolytic  dissocia- 
tion. Thus,  notwithstanding  the  excess  of  acid,  there  is  always 
enough  of  the  free  base  (hydro xyl-ions)  present  to  effect  the 
saponification. 

IV.  Thio-acids,  R- CO- SH,  and  Acid  Amides,  CnH2n+i-CONH2. 

96.  The  thio-acids  are  obtained  by  the  interaction  of  acid  chlo- 
rides and  potassium  hydrogen  sulphide,  KSH,  this  method  of 
formation  proving  their  constitution.  They  are  liquids  with  a  most 
disagreeable  odour,  and  when  heated  with  salts  of  heavy  metals 
yield  a  fatty  acid  and  the  corresponding  metallic  sulphide. 

Acid  amides  are  formed  by  the  action  of  ammonia  on  acid 
chlorides  or  anhydrides,  a  circumstance  which  affords  a  proof  of 
their  constitution: 

CnH2n+1  .CO!C1  +  H)NH2  =  CnH2n+i  .CONH2  +  HC1; 


•  CO 
CnH2n+i  -CO 


0  + 


NH< 


2CnH2n+1  .CONH2  +  H 


Acid  amides  are  also  formed  when  the  ammonium  salts  of  the 
fatty  acids  are  strongly  heated,  or  when  the  sodium  salts  are  dis- 
tilled with  ammonium  chloride,  one  molecule  of  water  being  elim- 
inated : 

CnH2n  ^  •  CO  [Q]NH2[HS1  -  CnH2n  ,t  -  CONH2  -f  H2O. 

When  the  nitriles  are  warmed  with  acids,  two  molecules  of 
water  are  taken  up,  with  formation  of  the  corresponding  acids  (79). 
This  reaction  can  be  so  modified  —  for  example  by  dissolving  the 
nitrile  in  concentrated  sulphuric  acid  —  that  only  one  molecule  of 
water  is  added,  when  amides  are  obtained: 


CnH2n+1  .CN  +  H20  =  CnH2n+1  .CONH2. 

The  acid  amides  are  therefore  intermediate  products  in  the  con- 
version of  nitriles  into  acids.  Distillation  with  such  a  dehydrating 
agent  as  phosphorus  pentoxide  converts  amides  into  nitriles  by 
elimination  of  water,  whereas  boiling  with  dilute  acids  or  alkalis 
produces  the  corresponding  acids  by  addition  of  the  elements  of 
water. 


128  ORGANIC  CHEMISTRY,  [§  97 

The  acid   amides   are  also  formed   by  the  action  of  ammonia 
upon  esters: 


CH3  •  CO  |OC2H5  +  H|  NH2  =CHS-  CONH2  4-  C2H5OH. 

The  acid  amides  are  solid,  crystalline  compounds,  with  the 
exception  of  the  liquid  formamide,  H«CONH2.  The  lower  members 
are  soluble  in  water,  and  odourless  when  pure.  Acetamide, 
CH3.CONH2,  melts  at  82°,  and  distils  at  222°.  Some  specimens 
have  a  strong  odour  suggestive  of  the  excrement  of  mice,  due  to 
slight  traces  of  impurities.  The  remarkably  high  boiling-point  of 
this  substance  is  worthy  of  notice. 

The  acid  amides  and  the  amines  greatly  differ  in  their  behaviour. 
Unlike  the  bond  between  carbon  and  nitrogen  in  the  amines,  that 

in  the  — C  <C  ATTT  -group  of  the  amides  is  readily  severed  by  boiling 

with  acids  or  alkalis.  Further,  the  basic  properties  of  ammonia  are 
greatly  weakened  by  the  exchange  of  one  of  its  hydrogen  atoms 
for  an  acid-radical;  and  although  salts  of  acid  amides  do  exist, 
they  are  decomposed  by  water.  Acetamide  hydrochloride, 
CHs  -CO*NH2  -HC1,  is  such  a  substance:  it  is  formed  by  passing  dry 
hydrochloric-acid  gas  through  an  ethereal  solution  of  acetamide. 
The  acid  amides  even  possess  acidic  properties:  an  aqueous  solu- 
tion of  acetamide  dissolves  mercuric  oxide,  forming  a  compound 
with  the  formula  (CH3-CONH)2Hg. 

The  behaviour  of  the  amides  and  amines  towards  nitrous  acid 
is  analogous,  the  corresponding  acids  and  alcohols  respectively 
being  produced  by  exchange  of  NH2  for  OH  (65). 

Amides  can  be  converted    into    primary  amines  by  a  method 
described  in  259. 

97.  Some  further  derivatives,  obtainable  from  the  acids  by 
substitution  in  the  carboxyl-group,  are  described  below. 

Amino-chlorides  are  produced  by  the  action  of  phosphorus  penta- 
chloride  on  the  acid  amides: 

R.CONH2  +  PC15  =  R.CC12.NH?  +  POC13. 

These  compounds  are  only  stable  when  one  or  both  of  the  hydrogen 
atoms  of  the  ami  no-group,  NH2,  are  replaced  by  alkyl-radicals. 


S  97]     'IMINO-COMPOUNDS,  HYDRAZIDES,  AND  AZIDES.         129 

They  yield  imino-chlorides,  R-CClrNH,  by  the  elimination  of  one 
molecule  of  HC1,  the  same  compounds  being  formed  by  the  addition 
of  HC1  to  nitrihs. 

Imino-ethers  have  the  constitution  R»C<JQ^,  and  may  be  re- 

garded as  the  product  of  the  replacement  of  the  doublv-linked  oxy- 
gen of  the  carboxyl-group  by  the  imino-group,  NH.  They  are  ob- 
tained by  combination  of  alcohols  arid  nitnles  under  the  influence 
of  dry  hydrochloric-acid  gas: 


The  well-crystallized  hydrochlorides  of  the  imino-ethers  are  con- 
verted by  treatment  with  ammonia  into  the  hydrochlorides  of  the 
amidines: 


R-  XTTT  r>    risl  NH»HC1 

* 


The  amidines  are  unstable  in  the  free  state,  but  are  strongly  mono- 
basic, and  form  stable  salts. 

Amidoximes  are  addition-products  of  the  nitriles  and  hydroxyl- 
amine,  NH2OH: 

R.CN+H2NOH  =R-C<^f  ' 

They  yield  salts  with  both  acids  and  bases,  and  give  a  flocculent, 
muddy-brown  or  green  precipitate  when  treated  with  an  alkaline 
solution  of  a  copper  salt,  a  reaction  which  affords  a  characteristic 
test  for  them 

Acid  hydrazides  are  produced  by  the  l  action  of  hydrazine, 
H2N  —  NH2,  on  acid  chlorides  or  esters,  and  therefore  have  the  con- 
stitution R.CONH-NH2.  Nitrous  acid  converts  them  into  add 
azides: 

R  .  CONH  .  NH2  +HN02  =  R  .  CON3  +2H20. 

The  acid  azides  are  volatile,  explosive  substances,  and  some  yield 
well-developed  crystals. 


ALDEHYDES  AND  KETONES. 

98.  Both  the  aldehydes  and  ketones  have  the  general  formula 
CnH2nO.  They  are  produced  by  the  oxidation  of  primary  and 
secondary  alcohols  respectively.  Both  classes  of  alcohols  have  the 
general  formula  CnH2n+2O,  so  that  each  oxidation  involves  the 
elimination  of  two  hydrogen  atoms. 

On  further  oxidation,  an  aldehyde  takes  up  one  oxygen  atom, 
forming  the  corresponding  acid  with  the  same  number  of  carbon 
atoms;  thus  CnH2nO  is  converted  into  CnH2n02.  It  follows  that 
an  aldehyde  is  an  intermediate  product  in  the  oxidation  of  an 
alcohol  to  an  acid  (45) : 

CnH2n+2O  — >  CnH2nO  — ->  CnH2nO2. 

Primary  alcohol          Aldehyde  Acid 

A  primary  alcohol  has  the  constitutional  formula  CnH2n+i  .CH2OH, 
and  on  oxidation  yields  an  acid  CnH2n+l  «COOH.  Since  in  this 
reaction  the  alkyl-group,  CnH2n+i,  is  not  altered,  it  must  be 
present  in  the  aldehyde.  Hence,  it  follows  that  the  two  hydrogen 
atoms  removed  from  the  alcohol  by  oxidation  must  belong  to  the 
group  —  CH/)H. 

Two  structural  formulae  are,  therefore,  possible, 

R-C^°     and     R-C— OH. 

The  improbability  of  the  existence  of  free  bonds  or  bivalent  carbon 
atoms  in  compounds  (16)  constitutes  a  strong  reason  against  the 
adoption  of  the  second  formula.  Moreover,  this  formula  points  to 
the  presence  in  an  aldehyde  of  a  hydroxyl-group:  in  reality,  the 
aldehydes  possess  none  of  the  properties  peculiar  to  substances 
containing  that  group.  For  example,  they  do  not  form  esters  or 

130 


§99]  ALDEHYDES  AND   KETONES.  131 

ethers,  and  phosphorus  pentachloride  does  not  replace  OH  by  Cl, 
but  effects  the  exchange  of  the  oxygen  atom  for  two  chlorine  atoms. 
Since  the  second  formula  does  not  represent  the  properties  of 
the  aldehydes,  it  follows  that  the  first  is  the  correct  one.  This 
view  is  supported  by  the  fact  that  aldehydes  are  formed  when  acid 
chlorides  dissolved  in  moist  ether  react  with  sodium,  the  chlorine 
atom  being  replaced  by  a  hydrogen  atom: 

k^Q   —  ^CsHy-C^Q. 

tt-Butyryl  chloride     n-Butyraldehyde 

The  aldehydes  therefore  contain  the  group 


99.  Ketones  result  from  the  removal  by  oxidation  of  two 
hydrogen  atoms  from  secondary  alcohols  (98)..  Like  the  alde- 
hydes, ketones  lack  the  properties  peculiar  to  hydroxyl-compounds, 
a  proof  that  one  of  the  hydrogen  atoms  removed  comes  from  the 
hydroxyl-group.  Putting  aside  the  possibility  of  the  formation  of 
free  bonds,  the  second  hydrogen  atom  eliminated  must  have  been 
attached  to  the  carbon  atom  linked  to  oxygen,  or  to  another  carbon 
atom.  The  two  cases  are  represented  below,  R  and  R'  being 
alkyl-groups: 

I.  II. 

CH^R          CH^R  GH^R          CHR 

II  |  |>0 

CHOH  ->  CO          or    CHOH  ->  CH    • 

CH2R'         CH2R'  CH2R'         CH2R' 

For  reasons  analogous  to  those  for  aldehydes,  formula  I.  is  more 
probable  than  formula  II.  The  products  obtained  by  the  oxida- 
tion of  ketones  indicate  that  formula  I.  represents  the  constitution 
of  this  class  of  compounds. 

The  general  formula  for  secondary  alcohols  is 

/H 

R  •  CIi2  •  G\~  CIi2  •  R  . 


From  such  an  alcohol  two  acids,  R-CH2»COOH  and  R/«CH2-COOH, 
are  obtained  by  strong  oxidation,  the  carbon  chain  in  some  of  the 
molecules  being  severed  to  the  right,  and  in  others  to  the  left,  of 


132  ORGANIC  CHEMISTRY.  .        [§  100 

the  CHOH-group.  This  reaction  furnishes  a  means  of  identifying 
the  alkyl-radicals  attached  to  the  group — CHOH — in  a  secondary 
alcohol.  Since  on  oxidation  ketones  yield  the  same  acids  as  the 
corresponding  secondary  alcohols,  the  alkyl-groups  of  the  secondary 
alcohols  must  remain  unchanged  in  the  ketones.  Hence,  such  a 
structure  as  that  represented  by  formula  II.  is  excluded,  so  that 
formula  I.  must  be  correct. 

Ketones  therefore  contain  the  carbonyl-group  CO  in  union  with 
two  carbon  atoms. 

Aldehydes  may  be  looked  upon  as  ketones  with  an  alkyl-group 
replaced  by  hydrogen. 

Nomenclature. 

The  name  aldehyde  is  derived  from  a/(cohol)  cfe/»/d(rogenatus), 
that  is,  "dehydrogenated  alcohol."  The  word  ketone  has  its 
origin  in  the  name  of  the  first  member  of  the  series,  acetone, 
GH3-CO-CH3  (in). 

The  aldehydes  are  named  after  the  corresponding  acids:  for- 
maldehyde,  H-CHO;  acetaldehyde,  CH3-CHO;  propionaldehyde, 
C2H5.CHO;  valeraldehyde,  C4H9.CHO;  etc. 

The  ketones  derive  their  names  from  the  alkyl-groups  which 
they  contain:  dimethylketone,  CH3-CO'CH3;  methylpropylketone, 
CH3.CO.C3H7;  etc. 

Methods  of  Formation. 

100.  Several  methods  besides  the  oxidation  of  alcohols  are 
applicable  to  the  preparation  of  both  aldehydes  and  ketones. 

1 .  Dry  distillation  of  the  salts  of  the  fatty  acids,  calcium  acetate 
yielding  acetone: 


CH3.|COO> 


The  conversion  of  acstic  acid  and  propionic  acid  into  the  cor- 
responding ketones  is  readily  effected  by  passing  the  vaporized  acids 
over  aluminium  oxide  heated  to  a  temperature  above  4003. 
When  an  equivalent  quantity  of  a  formate  is  mixed  with  the 
salt  of  the  other  fatty  acid,  an  aldehyde  is  produced  by  the  dis- 
tillation : 


C3H7.CO 
H 


ONa 
COONa 


O 


§  101]  ALDEHYDES  AND  KETONES.  f-j 

When  a  mixture  of  the  salts  of  two  different  fatty  acids,  excluding 
formates,  is  distilled,  mixed  ketones  are  obtained: 


CH..CO  ONa 

C2H5.[COONr  -C2H5+Na2C03. 


Methylethylketone 


2.  Aldehydes  or  ketones  can  be  obtained  from  compounds 
containing  two  halogen  atoms  linked  to  a  single  carbon  atom,  by 
heating  them  with  water: 


CH3.CH|C12  +  H,)0  =  CH3.CHO  +  2HC1. 

Ethylidene  chloride 

3.  When  primary  or  secondary  alcohols  in  the  gaseous  state  are 
passed  over  finely-divided  copper-dust,  obtained  by  reduction  of 
copper  oxide,  at  250°-400°,  they  yield  hydrogen,  and  aldehydes  or 
ketones  respectively: 

CnH2n+1.OH  =  H2+CnH2l,0. 

4.  An  important  method  for  the  preparation  of  ketones,  but 
not  of  aldehydes,  is  the  interaction  of  acid  chlorides  and  zinc  alkides: 
(?5)j   and   subsequent  decomposition   with  water.     An   addition- 
product  is  first  formed,  its  production  being  due  to  the  transforma- 
tion of  the  double  bond  of  the  oxygen  atom  into  a  single  one: 


/OZnCH3 


When   this  addition-product  is  treated  with  water  a  ketone  is 
formed  : 


O|Zn|CH3 


CnH2n+1  .C-CH3          +         =  CnH2n+1.CO.CH3+ZnO+CH4  + 
^[01  H|  +HC1. 

101.  Common  to  the  aldehydes  and  ketones  is  the  power  of 
forming  addition-products.  This  property  is  due  to  the  double 
bond  of  the  oxygen  atom,  the  conversion  of  which  into  a  single 
bond  sets  free  a  carbon  linking  and  an  oxygen  linking,  and  thus 


134  ORGANIC  CHEMISTRY.  [§  101 

enables  the  aldehydes  and  ketones  to  form  addition-products  with 
the  following  elements  and  compounds. 

1.  Hydrogen.  —  An  addition-product  is  produced  by  the  action  of 
sodium-amalgam  on  an  aqueous  solution  of  an  aldehyde  or  ketone; 
or  by  passing  the  vapour  of  the  aldehyde  or  ketone  mixed  with 
hydrogen  over  heated,  finely-divided  nickel.     Primary  alcohols  are 
formed  from  aldehydes,  and  secondary  from  ketones. 

2.  Sodium  hydrogen  sulphite.  —  When  aldehydes  or  ketones  are 
agitated  with  a  very  concentrated  aqueous  solution  of  this  com- 
pound, a  crystalline  addition-product  is  obtained: 

/OH 

C2H5.C<i;  +  NaHS03  =  C2H5.C^-OSO2Na. 

\H 

This  constitution  is  assigned  to  these  compounds  because  of  their 
ready  conversion  by  the  action  of  dilute  acids  or  sodium-carbonate 
solution  into  the  corresponding  aldehydes  or  ketones,  mere  solution 
in  water  effecting  this  decomposition  for  the  higher  members.  For 
this  reason,  it  is  highly  improbable  that  there  is  a  direct  bond 
between  sulphur  and  carbon  (59).  The  primary  sulphite  com- 
pounds —  sometimes  incorrectly  called  "  bisulphite  M  compounds  — 
dissolve  readily  in  water,  but  are  insoluble  in  very  concentrated 
solutions  of  the  acid  sulphite  itself. 

All  ketones  do  not  yield  these  addition-products.    They  are  most 

readily  obtained  from  those  containing  one  methyl-group  directly 

linked  to  carbonyl,  or  methylketones. 

The  use  of  primary  sulphite  is  often  exceedingly  serviceable 
for  the  purification  of  aldehydes  or  ketones,  or  for  separating  them 
from  reaction-mixtures. 

3.  Hydrocyanic  acid.  —  When  an  aldehyde  or  ketone  is  brought 
into  contact  with  anhydrous  hydrocyanic  acid,  and  a  drop  of  an 
alkaline    aqueous   solution    of   potassium    carbonate,    potassium 
cyanide,  or  a  similar  substance,  combination  takes  place: 


25 


On  addition  of  a  small  proportion  of  acid,  the  catalyst  is  rendered 
inoperative,  and  the  cyanohydrins  or  hydroxynitriles  formed  caii 
be  obtained  in  a  pure  state  by  vacuum-distillation.  This  syn- 


§§  102,  103]  ALDEHYDES  AND  KETONES.  135 

thesis  is  important,  since  the  cyanohydrins  can  be  converted  into 
hydroxy-acids  by  hydrolysis,  a  reaction  affording  a  means  of 
synthesizing  such  compounds  (179,  5). 

102.  With  GRIGNARD'S  alkyl  magnesium  halides  (75),  alde- 
hydes and  ketones  form  addition-products,  and  on  treatment  with 
water  these  yield  respectively  secondary  and  tertiary  alcohols: 


R.C^  +  R'.Mg.I  -  R.C-0-Mg.I, 
\R' 

Aldehyde  Addition-product 

H 

CO.Mg.I  +  2H2O  =  2R.CHOH.R'  +  MgI2  +  Mg(OH)2; 

-h  f  Secondary  alcohol 


Acetone  Addition-product 


Trimethylcarbinol 


103.  Other  reactions  common  to  aldehydes  and  ketones  depend 
upon  exchange  of  the  doubly-linked  oxygen  atom  for  other  atoms 


or  groups. 


groups. 

1.  Phosphorus  pentachloride  replaces  the  oxygen  atom  by  two 
chlorine  atoms. 

2.  Hydroxylamine  reacts  in  accordance  with  the  equation 


Oximzs  are  thus  produced,  and  are  called  aldoximes  when  derived 
from  aldehydes,  and  ketoximes  when  derived  from  ketones.  This 
reaction  is  of  very  general  application.  The  oximes  are  either 
crystalline  compounds,  or  liquids,  and  possess  both  acidic  and 
basic  properties.  When  .they  are  treated  with  bases,  the  hydrogen 
of  the  hydroxyl-group  is  replaced  by  a  metal;  with  acids,  addition- 
products  are  formed,  the  reaction  being  similar  to  the  production 
of  ammonium  salts: 

(CH3)2C=NOH.HC1. 

Acetoxime  hydrochloride 


136  ORGANIC  CHEMISTRY.  [§  105 

On  boiling  with  dilute  hydrochloric  acid,  the  oximes  take  up 
one  molecule  of  water,  yielding  hydroxylamine,  and  either  an  alde- 
hyde or  a  ketone. 

The  constitution  of  the  oximes  is  discussed  in  237. 
Energetic  reduction  converts  the  oximes  into  amines: 
R2C=NOH  +  4H  =  R2C  NH2  +  H2O. 
H 

The  aldoximes  are  readily  transformed  into  the  corresponding 
nitriles  by  the  action  of  dehydrating  agents,  such  as  acetic  anhy- 
dride: 

CnH2n+1  .C=NOH  ->  CnH2n+1  .C^N. 


Ketoximes  undergo  a  remarkable  rearrangement  of  the  atoms  in 
the  molecule  or  intramolecular  transformation,  called  after  its  dis- 
coverer the  "BECKMANN  transformation."  It  takes  place,  for 
example,  under  the  influence  of  acetyl  chloride.  The  ketoximes  thus 
yield  acid  amides,  with  substituents  in  union  with  the  nitrogen  atom  ; 

R-C.R' 

-*    R.CO-NHR'. 
NOH 

Oxime  Amide 

The  behaviour  of  aldehydes  and  ketones  with  phenylhydrazine,. 
C6H5NH-NH2  (310),  is  exactly  analogous  to  that  with  hydroxyl- 
amine: 


Phenylhydrazine  Phenylhydrazone 

The  substances  formed,  called  hydrazones,  are  either  well-defined 
crystalline  compounds,  or  liquids.  When  heated  with  hydrochloric 
acid,  they  take  up  the  elements  of  water,  forming  phenylhydrazine 
and  the  corresponding  aldehyde  or  ketone.  Phenylhydrazine  and 
hydroxylamine  are  important  reagents  for  detecting  the  presence 
of  the  carbonyl-group. 

The  constitution  of  the  phenylhydrazones  is  thus  established. 
Derivatives  of  phenylhydrazine  obtained  by  replacement  of  the 
hydrogen  of  the  immo-group,  —  NH,  by  an  alkyl-group,  react 
with  aldehydes  and  ketones  similarly  to  phenylhydrazine  itself,  so 


S  104]  ALDEHYDES.  137 

that  the  structure  R2C<  •  is  excluded.     This  is  rendered  even 

.N 


more  evident  by  the  fact  that  only  phenylhydrazines  containing 
an  unsubstituted  ammo-group  can  form  hydrazones. 

ALDEHYDES. 

104.  In  addition  to  the  properties  common  to  both  aldehydes 
and  ketones  (101-103),  aldehydes  havo  their  own  special  pro- 
perties. 

1.  Aldehydeammonia.  —  Acetaldehydeammonia  is  produced  from 
ammonia  and  acetaldehyde  : 


C2H4O  +  NH3  =  C2H4ONH3. 

Acetaldehyde  Acetaldehydeammonia 

It  is  precipitated  in  the  form  of  white  crystals  when  dry  ammonia- 
gas  is  passed  into  a  solution  of  acetaldehyde  in  anhydrous  ether, 
and  is  very  soluble  in  water.  Acids  decompose  the  aldehyde- 
ammonias  into  an  aldehyde  and  ammonia;  caustic  potash  is  unable 
to  effect  this  decomposition. 

At  ordinary  temperatures  the  molecular  formula  of  acetaldehyde- 
ammonia  is  three  times  its  empirical  formula.  When  dried  over 
sulphuric  acid,  it  loses  water  and  is  converted  into  (CH3«CHNH)3, 
(105)  a  polymeride  of  ethylidene-imine. 

2.  Acetals.  —  An  aldehyde  combines  with  two  molecules  of  an 
alcohol,  with  elimination  of  water,  and  production  of  an  acetal; 

>  PTT      prr  /  OC2H5  - 

<OC2H5  + 

Acetals  are  readily  obtained  by  addition  of  the  aldehyde  to  a  one 
per  cent,  solution  of  anhydrous  hydrochloric  acid  in  the  alcohol. 
The  reaction  is  not  complete;  it  is  limited  by  the  reverse  one,  since 
water  acts  on  acetal,  regenerating  aldehyde  and  alcohol.  Both  the 
formation  and  decomposition  of  acetal  are  considerably  accelerated 
by  the  presence  of  a  small  quantity  of  a  strong  mineral  acid,  which 
acts  as  a  powerful  catalyst.  The  acetals  are  liquids  of  aromatic 
odour,  and  distil  without  decomposition.  They  are  not  attacked 
by  alkalis,  but  are  resolved  by  acids  into  the  compounds  from  which 


138  ORGANIC  CHEMISTRY:  [§  105 

they  were  produced,  a  fact  which  supports  the  view  expressed  in 
the  above  structural  formula,  that  the  alkyl-groups  and  the  alde- 
hyde-residue are  indirectly  united  by  oxygen,  the  stability  of  a 
carbon  chain  being  sufficient  to  resist  the  action  of  such  reagents. 

3.  Reaction  with  acid  anhydrides. — Addition-products  are  ob- 
tained with  acid  anhydrides : 


rrr     r^- 
UM3«b^ 

Acetic  anhydride 

These  compounds  are  analogous  to  the  acetals.  They  are  easily 
decomposed  by  water,  and  still  more  readily  by  alkalis,  into  the 
corresponding  acid  and  aldehyde. 

105.  Two  kinds  of  addition-products  are  also  formed  by  the 
union  of  aldehyde  molecules  with  one  another.  When  a  few 
drops  of  concentrated  sulphuric  acid  are  added  to  acetaldehyde, 
a  liquid  boiling  at  22°,  the  mixture  becomes  warm,  and  then 
begins  to  boil  violently.  At  the  end  of  the  reaction  a  colourless 
liquid  is  obtained,  similar  to  the  original  one,  but  boiling  about 
100°  higher,  at  124°.  The  empirical  formula  of  this  compound  is  the 
same  as  that  of  acetaldehyde,  C2H4O,  but  its  vapour-density  is 
three  times  as  great,  so  that  it  has  the  molecular  formula  CeH^Os. 
This  substance,  paracetaldehijde,  is  readily  converted  into  acetal- 
dehyde by  distillation  with  dilute  sulphuric  acid,  another  example 
of  a  reaction  limited  by  the  reverse  one: 

C6H1203^3C2H40. 

The  equilibrium  reached  must  be  independent  of  the  nature  of  the 
acid,  that  is,  of  the  catalyst  ("  Inorganic  Chemistry,"  49),  as  has 
been  proved  for  this  reaction  by  experiment.  The  same  equilib- 
rium must  be  attained  without  the  aid  of  any  catalyst,  but  the 
change  proceeds  so  slowly  that  no  experimental  proof  has  yet  been 
possible.  A  direct  union  between  the  carbon  atoms  of  the  three 
aldehyde  molecules  in  paracetaldehyde  is  improbable,  and  the 
existence  of  an  indirect  linking  through  the  oxygen  atoms  must  be 
assumed,  because  it  accounts  for  the  ease  with  which  the  molecule 
of  paracetaldehyde  can  be  resolved.  The  compound  is  not  attacked 
by  sodium,  and  therefore  cannot  contain  hydroxyl-groups.  It 


106]  ALDEHYDES.  139 


lacks  all  the  characteristics  of  aldehydes,  proving  the  absence  of 
the  group  —  C  <:  ^. 
constitutional  formula 

CH3-C 


the  group  —  C  <:     .      These  properties  are  best  expressed  by  the 


H/°\H 


i     A 
X 

HCH3 


The  union  of  two  or  more  molecules  of  a  substance  to  form 
a  body  from  which  the  original  compound  can  be  regenerated  is 
called  polymerization. 

1  06.  Under  the  influence  of  dilute  alkali-solutions  aldehyde 
molecules  combine  with  production  of  compounds  of  a  different 
kind.  When  an  aqueous  solution  of  acetaldehyde  is  warmed  with 
concentrated  caustic  potash,  the  liquid  becomes  yellow;  after  a 
short  time,  reddish-yellow,  amorphous  masses  are  precipitated. 
The  aldehyde  has  resinificd,  and  the  reddish-yellow  substance 
formed  is  'called  aldehyde-resin.  When,  however,  dilute  caustic 
potash  (or  sodium  acetate,  zinc  chloride,  etc.)  is  added  to  acetalde- 
hyde, a  substance  is  formed  having  the  same  empirical  composition 
as  acetaldehyde,  but  with  double  the  molecular  formula,  C4H8O2. 
This  compound  is  called  aldol:  it  is  a  liquid,  distilling  without  de- 
composition under  diminished  pressure,  and  readily  undergoing  poly- 
merization. It  possesses  the  properties  characteristic  of  aldehydes, 
yielding  on  oxidation,  for  example,  an  acid  with  the  same  number 
of  carbon  atoms.  The  acid  thus  obtained  has  the  formula  C4H8O3, 
and  is  a  n-hydroxybutyric  acid;  that  is,  n-butyric  acid  with  one 
H-atom  of  the  alkyl-group  replaced  by  hydroxyl.  It  can  be  con- 
verted into  n-butyric  acid,  with  a  chain  of  four  carbon  atoms, 
proving  the  presence  of  a  similar  chain  in  aldol.  Hence,  in  this 
case,  the  union  of  the  aldehyde  molecules  has  been  effected 
through  the  carbon  bonds,  a  view  supported  by  the  fact  that  aldol 
cannot  be  reconverted  into  aldehyde.  The  combination  cf  the 
aldehyde  molecules  to  form  aldol  may  be  represented  by  the  equa- 
tion 


140  ORGANIC  CHEMISTRY.  [§  107 


2.. 
\OH 

Aldol 

This  constitutional  formula  expresses  the  properties  of  aldol. 

Instead,  of  explaining  the  formation  of  aldol  by  assuming  the 
combination  of  one  of  the  hydrogen  atoms  of  one  aldehyde  molecule 
with  the  oxygen  atom  of  another  to  form  hydroxyl,  it  might  be 
supposed  that  an  aldehyde  molecule  unites  with  a  molecule  of  water, 
the  addition-product  formed  reacting  with  a  second  molecule  of 
.aldehyde  with  elimination  of  water: 

H 


TT 

CH   C<°-3—  ? 

|OH  +  H|CH,.CHO  -  CH3.C  <cH2 

Aldol 

Reactions  are  often  explained  by  assuming  the  formation  of  such 
addition-products  and  the  subsequent  elimination  of  water.  In  a 
few  instances  this  view  has  been  experimentally  verified. 

Aldol  is  both  an  alcohol  and  an  aldehyde,  hence  its  name, 
a/d(ehyde-alcoh)oZ.  The  union  of  molecules  through  carbon  bonds, 
as  in  the  formation  of  aldol,  with  the  production  of  compounds 
from  which  the  original  substance  cannot  be  regenerated  by  any 
simple  method,  is  called  condensation. 

It  is  probable  that  aldehyde-resin  is  a  product  resulting  from 
continued  condensation  of  the  aldol  molecules  with  elimination  of 
water,  just  as  aldol  itself  readily  loses  one  molecule  of  water  when 
heated,  with  formation  of  crotonaldehyde  (142)  : 

CH3.CHOH.CH2.CQ-H20=CH3.CH:CH.CQ. 

Aldol  Crotonaldehyde 

The  mechanism  of  the  condensation  of  the  higher  aldehydes 
always  involves  transposition  of  a  hydrogen  atom  linked  to  the 
carbon  atom  carrying  the  aldehyde-group  of  one  molecule,  this 
hydrogen  combining  with  the  carbonyl-oxygen  of  another  molecule 


|§  107,  108]  FORMALDEHYDE.  141 

to  form  hydroxyl,  the  liberated  carbon  valencies  being  simulta- 
neously saturated: 


,.        c>CmIW  =  CnH2n+1.CH.CHOH.CnJWi. 
CH  ITT 

0  co 


Tests  for  Aldehydes. 

107.  The  following  tests  serve  for  the  detection  of  aldehydes. 

1.  Resinification  with  alkalis. 

2.  Reduction  of  an  ammoniacal  silver  solution.     This  solution 
is  prepared  by  adding  excess  of  caustic  potash  to  a  solution  of 
silver  nitrate,  and  then  just  sufficient  ammonia  to  dissolve  the 
precipitated   silver  oxide.     When   this   liquid   is  brought   into   a 
dilute  aqueous  solution  of  an  aldehyde,  and  the  mixture  warmed, 
a  beautiful  mirror  of  metallic  silver  is  deposited  on  the  sides  of 
the  tube. 

3.  When  an   aldehyde    is    added    to    a   solution    of   magenta 
decolorized  by  sulphurous  acid — SCHIFF'S  reagent — the  red  colour 
is  restored. 

Formaldehyde,  H-C^Q. 

1 08.  Formic  acid,  the  first  member  of  the  homologcus  series  of 
fatty  acids,   has  certain  properties  not  possessed  by  the  higher 
members  (81).     Formaldehyde  affords  another  striking  example  of 
this  phenomenon  of  disparity  between  the  first  and  succeeding 
members  in  a  homologous  series. 

It  is  obtained  by  the  oxidation  of  methyl  alcohol,  effected  by 
passing  a  mixture  of  air  and  methyl-alcohol  vapour  over  a  hot 
spiral  of  platinum  or  copper.  The  heat  produced  by  the  reaction 
is  sufficient  to  raise  the  temperature  of  the  spiral  to  redness,  and 
to  maintain  it  at  that  point,  provided  the  stream  of  gas  is  passed 
'Over  it  with  sufficient  velocity.  The  formaldehyde  produced  is 
absorbed  by  water,  in  which  it  dissolves  readily. 

This  aldehyde  is  a  product  of  the  incomplete  combustion  of 
wood,  peat,  and  many  other  organic  substances.  This  fact 


142  ORGANIC  CHEMISTRY.  [§  108 

explains  its  presence  in  traces  in  the  atmosphere,  especially  in 
that  of  large  towns.  Its  formation  from  methane  and  ozone  is 
also  noteworthy. 

Formaldehyde  has  a  very  pungent  odour.  At  ordinary  tem- 
peratures it  is  gaseous,  but  when  cooled  with  solid  carbon  dioxide 
and  ether,  it  forms  a  liquid  boiling  at  —  20°.  Even  at  this  tem- 
perature polymerization  begins,  and  at  higher  temperatures  it 
proceeds  with  explosive  energy.  When  the  aqueous  solution  is 
evaporated,  paraformaldehyde,  a  crystalline  polyjneride  of  unknown 
molecular  weight,  is  produced.  It  melts  at  JBT  '  On  concentrat- 
ing a  solution  of  formaldehyde  with  strong  sulphuric  acid,  only 
part  of  the  formaldehyde  is  evolved  as  gas;  the  rest  polymerizes, 
and  remains  as  a  white,  crystalline  mass,  a  mixture  of  a-,  /?-,  and 
f-polyoxymethylene.  The  molecular  weights  of  these  polymerides 
are  not  known:  on  heating,  they  are  reconverted  into  formalde- 
hyde, proving  them  true  polymerides.  Prolonged  heating  of  the 
/--variety  with  water  yields  another  polymeride,  d-polyoxymethylene. 
On  treatment  with  ammonia  at  the  ordinary  temperature,  formal- 
dehyde does  not  yield  an  aldehydeammonia,  but  a  complicated 
compound,  CeH^N^,  hexamethylenetetramine,  (CH2)6N~4,  a  crys- 
talline, very  hygroscopic,  basic  substance,  employed  as  a  medicine 
under  the  name  "  urotropine."  At  120°-  160°  and  increased 
pressure,  methylamines  are  formed  : 


+  3CH2O=2NH2.CH3 
2NH3  +  6CH2O  =  2NH  (CH3)  2  +  2CO2  +  2H2O  ; 
+  9CH2O=2N(CH3)3  +  3C02 


When  treated  with  potassium  hydroxide,  formaldehyde  does 
not  resinify,  but  is  converted  into  methyl  alcohol  and  formic 
acid: 

2CH20  +  H2O  =CH3OH  +  HCOOH. 

When  a  fifteen  per  cent,  solution  of  formaldehyde  is  mixed 
with  an  equal  volume  of  a  solution  of  sodium  hydroxide,  and  a 
small  proportion  of  cuprous  oxide  added,  formic  acid  is  produced, 
with  evolution  of  hydrogen: 


§  109]  ACETALDEHYDE.  143 

The  oxime  of  formaldehyde  also  polymerizes  readily.  For- 
maldehyde and  its  derivatives  display  a  much  greater  tendency 
towards  polymerization  than  the  other  aldehydes  and  their  deriva- 
tives, and  differ  from  them  in  their  behaviour  with  ammonia  and 
with  caustic  potash. 

An  aqueous  solution  containing  40  per  cent,  of  formaldehyde 
is  a  commercial  product,  and  is  called  "formalin."  After  dilution, 
it  is  employed  as  a  disinfectant,  and  in  the  preservation  of  ana- 
tomical specimens.  It  possesses  the  remarkable  property  of  con- 
verting protein  substances  into  a  hard,  elastic  mass,  quite  insol- 
uble in  water.  The  contents  of  a  hen's  egg,  for  example,  undergo 
this  transformation  through  contact  with  formalin  for  half-an- 
hour;  brain-substance  attains  the  consistency  of  india-rubber; 
and  a  solution  of  gelatin  is  converted  into  a  hard,  transparent,  in- 
soluble, odourless  mass,  reducible  to  a  fine  powder.  Before 
development,  photographic  films  with  a  basis  of  galatin  are 
immersed  in  a  dilute  solution  of  formaldehyde  for  a  short  time 
to  render  the  gelatin  insohible. 

The  condensation  of  formaldehyde  is  discussed  in  206. 

The  concentration  of  a  formalin  solution  is  determined  by  adding 
excess  of  a  solution  of  twice  normal  sodium  hydroxide,  and  then 
hydrogen  peroxide,  the  formaldehyde  being  converted  completely 
into  formic  acid.  The  excess  of  alkali  is  estimated  by  titration,  and 
from  the  result  the  amount  of  formaldehyde  can  be  calculated, 
since  one  molecule  of  the  aldehyde  yields  one  molecule  of  the  acid. 

Acetaldehyde,  CH3.C^. 

109.  Acetaldehyde  is  the  typical  aldehyde  of  this  series,  since 
it  has  all  the  properties  characteristic  of  aldehydes  as  a  class.  It 
is  obtained  by  the  oxidation  of  ethyl  alcohol  by  means  of  potassium 
dichromate  and  sulphuric  acid,  and  is  a  liquid  with  a  disagreeable 
odour,  at  least  in  the  dilute  state:  it  boils  at  22°,  and  solidifies  at 
—  120-6°.  It  readily  polymerizes  to  paracetaldehyde,  CeH^Os 
(105),  or  to  metacetaldehyde.  The  molecular  weight  of  this 
product  is  not  known  with  certainty,  but  cryoscopic  determina- 
tions point  to  the  formula  (C2H4O)4,  or  a  polymeric  multiple  of 
it.  Metacetaldehyde  forms  well-developed,  acicular  crystals, 


144  ORGANIC  CHEMISTRY.  [§  109 

which  begin  to  sublime  at  150°.  Neither  it  nor  paracetaldehyde 
exhibits  the  aldehyde  reactions;  for  example,  neither  is  resinified 
by  alkalis. 

The  inter-relationship  of  acetaldehyde,  paracetaldehyde,  and 
metacetaldehyde  is  still  a  matter  of  doubt,  but  certain  facts  have 
been  definitely  established.  Acetaldehyde  is  converted  into  par- 
acetaldehyde by  the  action  of  various  catalysts,  among  them  sul- 
phuric acid  at  ordinary  or  somewhat  higher  temperature,  met- 
acetaldehyde being  also  produced  in  small  proportion.  If  the  liquid 
is  strongly  cooled  immediately  after  addition  of  the  catalyst, 
metacetaldehyde  is  the  main  product,  and  crystallizes  out  in  well- 
developed  needles,  but  paracetaldehyde  is  also  formed.  If  the 
temperature  rises,  metacetaldehyde  is  decomposed  under  the 
influence  of  the  catalyst,  with  production  of  acetaldehyde  and  par- 
acetaldehyde. No  direct  transformation  of  metacetaldehyde  into 
paracetaldehyde  has  been  observed,  the  mechanism  of  the  trans- 
formation probably  involving  a  preliminary  complete  depolymeriza- 
tion  to  acetaldehyde,  followed  by  the  formation  of  paracetaldehyde. 

Addition  of  a  very  small  proportion  of  sulphuric  acid  to  ice-cold 
acetaldehyde  generates  metacetaldehyde,  but,  on  further  addition 
of  sulphuric  acid,  the  metacetaldehyde  disappears,  and  paracetal- 
dehyde is  formed.  Calcium  chloride,  a  much  less  energetic  catalyst, 
also  induces  the  formation  of  metacetaldehyde,  paracetaldehyde 
being  produced  only  in  traces.  The  equilibrium  between  acetal- 
dehyde and  metacetaldehyde  is,  therefore,  much  more  readily 
attained  than  that  between  acetaldehyde  and  paracetaldehyde. 
The  predominance  of  paracetaldehyde  or  metacetaldehyde  in  the 
ternary  system 

Paracetaldehyde  ^  Acetaldehyde  <=^  Metacetaldelryde 

is  dependent  on  the  experimental  conditions,  temperature  being  a 
very  important  factor. 

In  practice,  acetaldehyde  is  transformed  into  paracetaldehyde 
by  addition  of  sulphuric  acid,  the  catalyst  being  rendered  inopera- 
tive by  neutralization  of  the  acid  after  completion  of  the  reaction. 
The  acetaldehyde  and  paracetaldehyde  can  then  be  readily  separated 
by  distillation.  Inversely,  the  conversion  of  paracetaldehyde  into 
acetaldehyde  is  effected  by  addition  of  sulphuric  acid,  and  dis- 
tillation of  the  mixture  from  a  water-bath.  The  volatilization  of  the 
acetaldehyde  upsets  the  equilibrium,  causing  the  catalyst  to  decom- 
pose a  fresh  portion  of  paracetaldehyde.  The  acetaldehyde  thus 


§  110]  KETONES.  145 

produced  distils,  and  the  process  continues  until  the  conversion  into 
acetaldehyde  is  complete. 

In  preparing  metacetaldehyde,  the  acetaldehyde  is  cooled  to  a 
low  temperature,  and  dilute  sulphuric  acid  added.  Metacetalde- 
hyde crystallizes  out,  and  can  be  isolated  by  filtration.  The 
mode  of  reconverting  it  into  acetaldehyde  is  similar  to  that  described 
for  paracetaldehyde. 

KETONES. 

no.  The  properties  characteristic  of  the  ketones  are  described 
in  101-103.  The  first  member  of  the  homologous  series  cannot 
contain  less  than  three  carbon  atoms. 

Ketones  have  the  general  formula  R»CO«R',  and  are  always 
divided  at  the  carbonyl-group  by  oxidation  (99) ;  that  is,  oxida- 
tion occurs  at  that  part  of  the  molecule  already  containing  oxygen 
(45) .  The  decomposition  can,  however,  take  place  in  two  different 
ways: 

Ri|CO.R'     or    R.CO-IR'. 
i  ii 

Thus,  methylnonylketone,   CH3-|CO-|C9H19,  can  yield  formic 

i       ii 

acid,  CH2O2,  and  capric  acid,  C^H^C^;  or  acetic  acid,  C2H4O2, 
and  pelargonic  acid,  C9H18O2;  the  decomposition  taking  place  at 
the  points  indicated  by  the  lines  I.  and  II.  respectively.  The  oxida- 
tion is  such  that  the  decomposition  takes  place  at  both  points 
simultaneously,  so  that  four  acids  are  obtained.  Two  of  them  may 
be  identical;  for  example,  the  oxidation  of  methylethylketone, 
CH3-CO-C2H5,  produces  acetic  acid  and  acetic  acid  by  decom- 
position at  point  II.,  and  formic  acid  and  propionic  acid  by  decom- 
position at  I.  Usually  the  reaction  which  leaves  the  carbonyl  in 
union  with  the  smallest  alkyl-residue  predominates.  Oxidation 
therefore  affords  a  means  of  determining  the  position  of  the  car- 
bonyl-group in  the  ketone  molecule. 

The  ketones  are  further  distinguished  from  the  aldehydes 
by  their  behaviour  towards  ammonia :  this  reaction  has  been  care- 
fully investigated  for  acetone,  the  first  member  of  the  series.  By 
elimination  of  water  it  yields  complicated  substances,  such  as 
diacetoneamine ,  C6H13NO  or  (2C3H6O  +  NH3  — H2O),  triacetone- 
aminc,  C9H17XO  or  (3C3H6O  +  NH3-2H20),  and  so  on. 


14G  ORGANIC  CHEMISTRY.  [§  111 

The  ketones  do  not  yield  polymerides,  but  are  capable  of  form- 
ing condensation -products. 

Acetone,  CH3.CO.CH3. 

in.  Acetone  is  prepared  on  the  manufacturing  scale  from 
crude  wood-spirit  (42),  and  by  the  dry  distillation  of  calcium  ace- 
tate. It  is  present  in  very  small  quantities  in  normal  urine,  but 
in  much  greater  proportion  in  pathological  cases,  such  as  diabetes 
mellitus  and  acetonuria.  It  is  a  liquid  of  peculiar,  peppermint-like 
odour,  boils  at  56 -3°,  solidifies  at  —94-9°,  and  has  a  specific  gravity 
of  0-812  at  0°.  It  is  an  excellent  solvent  for  many  organic  com- 
pounds, and  is  miscible  in  all  proportions  with  water;  on  addition 
of  certain  salts,  such  as  potassium  carbonate,  the  liquid  separates 
into  two  layers.  It  is  converted  by  reduction  into  tsopropyl 
alcohol  (150),  and  yields  a  crystalline  oxime  melting  at  69°. 
Condensation-products  derived  from  acetone  are  considered  in  143 
and  285. 

Sulphonal,  an  important  soporific,  is  prepared  from  acetone.  In 
presence  of  hydrochloric  acid,  acetone  unites  with  ethylmercaptan 
with  elimination  of  water: 

(CH3)2CO+2HS.C2H6  -  (CH3)2C(SC2H6)2  +  H2O. 

Dimethyldiethyl- 
mercaptole 

Oxidation  with  potassium  permanganate  converts  the  two  sulphur 
atoms  of  this  compound  into  SO2-groups,  forming  diethylsulphonedi- 
methylmethane,  (CH3)2C(S02C2H5)2,  or  sulp'honal.  It  crystallizes  in 
colourless  prisms,  soluble  with  difficulty  in  cold  water,  and  melting 
at  126°. 


UNSATURATED  HYDROCARBONS. 


I.  ALKYLENES   OR  OLEFINES,  CnH2n. 

Methods  of  Formation. 

112.  1.  The  ole  fines  are  formed  in  the  dry  distillation  of  com- 
plicated carbon  compounds,  a  fact  which  accounts  for  their  pres- 
ence to  the  extent  of  4-5  per  cent,  in  coal-gas. 

2.  By  elimination  of  the  elements  of  water  from  the  alcohols 


This  can  sometimes  be  effected  by  heat  alone,  as  with  tertiary 
alcohols,  but  it  is  usually  necessary  to  warm  the  alcohol  with  a 
dehydrating  agent,  such  as  concentrated  sulphuric  acid  (54  and 
115)  or  zinc  chloride.  Water  is  more  readily  eliminated  from  the 
secondary  and  tertiary  alcohols  than  from  the  corresponding  pri- 
mary compounds. 

3.  By  abstraction  of  hydrogen  halide  from  alkyl  halides,  effected 
by  heating  with  alcoholic  potash,  a  solution  of  caustic  potash  in 
alcohol  : 


CnH2n+1I  +  KOC2H5  =  CnH2n  +  KI  +  C2H5OIL 
An  ether  is  also  formed  (55)  : 

CnH2n+1I  +  KOC2H5  =  CnH2n+1OC2H5  +  KI. 

With  alkyl  iodides  the  reaction  chiefly  follows  the  first  equation, 
the  secondary  and  tertiary  iodides  being  specially  adapted  for  the 
production  of  unsaturated  hydrocarbons. 

147 


148 


ORGANIC  CHEMISTRY. 


[§  113 


Name. 

Formula. 

Boiling- 

Name. 

Formula. 

Boiling- 

point. 

point. 

Ethylene.  .  .  . 

C2H4 

-103° 

Heptylene  .  . 

C7H14 

98° 

Propylene.  .  . 

C3H6 

-  48° 

Octylene.  .  .  . 

124a 

n-Butylene.  . 
n-Amylene.  .  . 

C4H8 
C5H10 

-     5° 
39° 

Nonylene.  .  . 
Decylene.  .  .  . 

C9H18 

Crf 
JQX12Q 

153° 
172° 

Hexylene.  .  .  . 

68° 

Undecylene. 

195° 

The  names  of  the  members  of  this  series  are  derived  from  those 
of  the  saturated  hydrocarbons  by  altering  the  termination  "ane  " 
to  "ylene."  These  compounds  are  denoted  by  the  general  name 
alkylenes  or  olefines. 

To  indicate  the  position  of  the  double  bond  in  the  molecule, 
the  alkylenes  are  sometimes  regarded  as  substituted  ethylenes: 
thus,  CH3.CH:CH.CH3  is  called  symmetrical  dimethylethylene; 
and  (CH3)2C:CH2,  unsymm,etrical  dimethylethylene. 

Properties. 

113.  The  lowest  members  of  this  homologous  series  are  gases, 
and  are  slightly  soluble  in  water:  the  higher  members  are  liquids 
or  solids,  insoluble  in  water,  but  soluble  in  alcohol  and  ether.  At 
their  melting-points  the  specific  gravities  of  the  lower  members 
are  about  0-63,  rising  with  increase  in  the  number  of  carbon 
atoms  to  about  0«79.  They  are  only  slightly  higher  than  those 
of  the  corresponding  saturated  hydrocarbons;  but  their  refrac- 
tions are  much  higher  (120).  Like  the  saturated  hydrocarbons, 
the  olefines  are  colourless. 

Their  most  important  chemical  property  is  the  power  of  form- 
ing addition-products,  and  on  account  of  it  they  are  said  to  be 
unsaturated.  Addition-products  are  very  readily  obtained  by  the 
action  of  the  halogens,  especially  bromine,  on  the  olefines  and 
other  substances  containing  a  double  bond,  the  presence  of  which 
can  be  detected  by  the  decolorization  of  bromine-water.  Another 
test  for  the  presence  of  a  double  bond,  suggested  by  VON  BAEYER, 
is  carried  out  by  agitating  the  substance  with  a  dilute  solution  of 
potassium  permanganate  and  sodium  carbonate.  Owing  to  the- 
reducing  action  of  compounds  containing  a  double  carbon  bond, 
the  Violet  colour  of  the  permanganate  quickly  disappears,  with 
formation  of  a  brown-red,  flocculent  precipitate  of  hydra  ted  man- 
ganese dioxide.  Compounds  of  other  classes^  such  as  aldehydes, 


§  114]  OLEFINES.  149 

react  similarly  with  potassium  permanganate,  so  that  the  test  can 
only  be  applied  in  their  absence  to  hydrocarbons,  unsaturated 
acids,  and  a  few  other  substances. 

The  hydrogen  halides  react  by  addition  with  the  olefines  to 
form  the  alkyl  halides,  hydriodic  acid  combining  very  readily. 

Concentrated  sulphuric  acid  yields  the  alkylsulphuric  acids  by 
addition:  it  is  sometimes  necessary  to  employ  the  fuming  acid. 
The  addition  of  sulphuric  acid,  like  that  of  the  hydrogen  halides, 
results  in  the  union  of  the  acid-residue  with  the  unsaturated  carbon 
atom  linked  to  the  smallest  amount  of  hydrogen.  For  example, 

CH 

isobutylene,  prr3  >C:CH2,  treated  with  sulphuric  or  hydriodic.  acid 

yields 

CHo     r    pw  CHo     n    pw 

C\TJ     ^>^-' — ^113  r\Tj    s>^      ^-n.3- 

Utl3        |  Orl3        j 

OSO3H  I 


This  reaction  may  be  otherwise  expressed  by  stating  that  there 
is  a  tendency  for  the  number  of  methyl-groups  to  increase  in  such 
.addition-reactions. 

Hypochlorous  acid,  Cl-OH,  can  also  form  addition-products 
which  are  chloro-alcohols: 


=  CH2C1.CH2OH. 

Ethylene  Glycolchlorohydrin 

114.  Olefines  can  form  condensation-products,  butylene  and  the 
amylenes  yielding  them  on  treatment  with  moderately  dilute  sul- 
phuric acid,  although  ethylene  cannot  be  similarly  condensed.  The 
-condensation  may  be  explained  by  assuming  that  an  addition- 
product  with  sulphuric  acid,  or  alkylsulphuric  acid,  is  first  formed, 
and  then  reacts  with  a  second  molecule  of  the  olefine: 

r  (CH3)2C-CH3 

XS3>C:CH2-+  J  _  ,  :-* 

CHs  JOSQ3H  +  H|HC:C(CH3)2? 

(CH3)2C-CH3 

HC=C(CH3)2. 

The  simplest  member  of  this  series,  CH2,  methylene,    has    not 


150  ORGANIC  CHEMISTRY.  [§  115 

been  obtained.  Various  attempts  have  been  made  to  prepare  it: 
for  instance,  by  the  elimination  of  HC1  from  methyl  chloride. 
Such  experiments  have  always  resulted  in  the  formation,  not  of 
methylenc,  but  of  ethylene,  two  CH2-groups  uniting  to  form  a 
single  molecule. 

Ethylene,  C2H4. 

115.  Ethylene  is  a  gas,  and  is  usually  prepared  by  heating  a 
mixture  of  ethyl  alcohol  and  sulphuric  acid.  Ethylsulphuric  acid 
is  first  formed  (54),  and  on  further  heating  decomposes  into  ethyl- 
ene and  sulphuric  acid: 


In  the  preparation  of  ether  (56)  the  temperature  is  maintained 
below  a  certain  limit,  and  fresh  alcohol  is  continually  added, 
but  in  this  reaction  a  higher  temperature  is  employed,  and 
no  alcohol  is  added.  At  the  temperature  of  the  reaction, 
sulphur  dioxide  and  carbon  dioxide  are  produced,  but  can  be 
removed  from  the  ethylene  by  passing  it  through  dilute  alkali. 

It  has  been  customary  to  add  sand  to  the  mixture  of  alcohol 
and  sulphuric  acid  in  the  flask,  with  a  view  to  prevent  undue  foam- 
ing of  the  liquid.  SENDERENS  has  proved  that  the  sand  exerts  a 
catalytic,  accelerating  influence,  producing  a  more  vigorous  evolu- 
tion of  gas  at  a  lower  temperature.  Addition  of  5  g.  of  anhydrous 
aluminium  sulphate  per  100  c.c.  of  liquid  is  even  more  effective, 
and  also  practically  eliminates  the  tendency  to  foaming. 

A  purer  product  is  obtained  by  passing  the  vapour  of  ethyl 
alcohol  over  clay  balls  heated  at  300°-400°,  water  and  ethylene 
being  formed.  When  passed  over  aluminium  oxide  at  400°, 
ether-vapour  also  gives  a  good  yield  of  water  and  ethylene. 

Ethylene  can  also  be  prepared  from  ethylene  bromide,  C2H4Br2, 
by  removal  of  its  two  bromine  atoms,  which  is  effected  by  bringing 
it  into  contact  with  GLADSTONE  and  TRIBE'S  copper-zinc  couple. 

Ethylene  possesses  a  peculiar,  sweetish  odour,  and  burns  with 
a  luminous  flame.  It  is  slightly  soluble  in  water  and  in  alcohol. 
When  passed  into  bromine  it  is  quickly  converted  into  ethylene 


§§116,  117]  THE  NATURE  OF  THE  DOUBLE  CARBON  BOND.    151 

bromide,  C2H4Br2  (148).  It  is  readily  absorbed  by  concentrated 
sulphuric  acid  at  170°,  with  formation  of  ethylsulphuric  acid. 
SABATIER  found  that  a  mixture  of  hydrogen  and  ethylene  is 
changed  completely  into  ethane  when  passed  over  finely-divided 
nickel  at  temperatures  of  less  than  300°  (28) . 

Amylenes,  C^H^. 

116.  A  mixture  of  isomeric  amylenes  and  pentane  is  technically 
prepared  by  heating  fusel-oil  (43)  with  zinc  chloride. 

The  isomeric  amylenes  can  be  separated  by  two  methods,  also 
applicable  in  other  similar  cases.  One  is  based  on  the  solu- 
bility at  a  low  temperature  of  some  of  the  isomerides  in  a  mixture 
of  equal  volumes  of  water  and  concentrated  sulphuric  acid,  with 
formation  of  amylsulphuric  acids;  the  other  isomerides  are  insol- 
uble. This  treatment,  however,  converts  part  of  the  amylenes  into 
condensation-products,  called  diamylene  arid  triamylene.  The  other 
mode  of  separation  depends  upon  the  different  velocities  with  which 
the  isomeric  amylenes  form  addition-products  with  hydriodic  acid. 

The  Nature  of  the  Double  Carbon  Bond. 

117.  Hitherto  the  existence  of  a  double  carbon  bond  in  the 
alkylenes  has  been  arbitrarily  assumed:    the  constitution  of  un- 
saturated  compounds  could,  however,  be  represented  in  a  variety 
of  ways. 

1 .  Existence  of  bivalent  or  tervalent  carbon  atoms: 

ii  in         in 

CH3— C— CH3,        CH2— CH— CH3. 


2.  Existence  of  free  bonds: 

a.  On  one  carbon  atom  only: 


GIL 


-£— CH3. 


b.  On  different  carbon  atoms: 


—  CH  —  C 

i 


152  ORGANIC  CHEMISTRY.  [§  117 

3.  Existence  of  a  double  carbon  bond: 

CH3—  CH=CH2. 

4.  Existence  of  a  closed  chain  or  ring: 

CH2— CH2. 

\X 

CH2 

It  is  stated  in  113  that  unsatura ted  compounds  are  convertible 
into  saturated  compounds  by  addition  of  atoms  or  groups.  The 
constitution  of  these  addition-products  on  the  one  hand,  and  the 
method  of  formation  of  the  unsatura  ted  products  obtained  by  the 
elimination  of  a  hydrogen  halide,  etc.,  from  the  saturated  com- 
pounds on  the  other,  enable  a  decision  to  be  arrived  at  between 
these  four  possibilities. 

It  should  be  observed  that  the  addition-product  is  the  same. 
whether  the  existence  of  a  bivalent  carbon  atom,  or  of  two  free 
bonds  on  the  same  carbon  atom,  be  assumed.  Thus,  whether 

ii 
propylene  be  supposed  to  have  the  constitution  CH3-C-CH3  or 

CH3-C-CH3,  the  addition  of  bromine  produces  the  same  substance, 

CH3.CBr2.CH3.     Similarly,   the  assumption  of  tervalent    carbon 
atoms,  or  of  free  bonds  on  different  carbon  atoms,  leads    to  the 

in      in 
same   result;     CH2-CH2   with  two   tervalent   carbon   atoms,  and 

CH2-CH2  with  free  bonds,  yielding  with   bromine  the  same  addi- 

I  '  I 

tion-product,  CH2Br-CH2Br.     It  follows  that  for  the  present  it  is 
unnecessary  to  treat  cases  1  and  2  separately. 

It  is  readily  proved  that  addition  does  not  take  place  at  only 
one  carbon  of  unsaturated  compounds,  for  otherwise  ethylene 
chloride,  C2H4C12,  would  have  the  constitution  CH3-CHC12,  and 
ethylene  itself,  CH3-CH.  Ethylene  chloride  would  then  be  iden- 
tical with  the  product  obtained  by  the  action  of  phosphorus  penta- 
chloride  upon  acetaldehyde,  CH3-CHO,  since  the  exchange  of 
the  oxygen  atom  in  the  latter  for  twro  chlorine  atoms  yields  a  com- 
pound of  the  formula  CH3-CHC12.  But  ethylene  chloride  is  differ- 
ent from  the  compound  C2H4C12  (ethylidene  chloride)  got  from  aide- 


§  118]        THE  NATURE  OF  THE  DOUBLE  CARBON  BOND.        153 

hyde.  Similarly,  propylene  chloride,  C3H6C12,  formed  by  the 
addition  of  chlorine  to  propylene,  is  not  identical  with  the  reaction- 
product  obtained  by  treating  acetone  with  phosphorus  penta- 
chloride,  CH3-CC12-CH3  (chloroacetone)  ',  nor  with  that  from  pro- 

pionaldehyde,   OH3-CH2-CHC12    (propylidene  chloride').     Ethylene 

ii 

therefore  cannot  have  either  the  formula  CH3-CH  or  CH3-CH. 

A 

nor  propylene  any  of   the   formula?  CH3-C-CH3,   CH3-OH2.CH, 

CHg-C-CHg,  or  CH3.CH2.CH. 

118.  A  further  insight  into  the  structure  of  the  unsaturated  com- 
pounds is  derived  from  other  considerations.  Propylene  is  obtained 
by  the  elimination  of  PII  from  n-propyl  iodide,  CH3«CH2-CH2I. 
The  same  compound  is  produced  by  the  removal  of  Hi  from  iso- 
propyl  iodide,  CH3-CHI-CH3.  Hence,  it  follows  that  propylene 


cannot  have  either  the  formula  CH2-CH2-CH2  or    \    /      ,  and 

Ii  \' 

I  CH2 

therefore      the      remaining      possibilities      are      CH3-CH'CH2, 

in     in 
CH3-CH.CH2>  and  CH3.CH:CH2. 

isoButylene,  C4H8;  is  similarly  formed  by  the  elimination  of 
HI  from  both  isobutyl  iodide,  (CH3)2C|H)CH2jT],  and  tertiary  butyl 

iodide,  (CH3)  2C  |T|  •  CH2|HJ  .     Thus,  ^'sobutylene  can  only  have  one  of 

in  in 
the    formula?    (CH3)2C.OH2,    (CH3)2O.CH2,    and     (CH3)2C:CH2. 

I    I 

Both  these  examples  indicate  that  the  removal  of  hydrogen  halide 
from  an  alkyl  halide  necessitates  the  elimination  of  a  halogen  atom 
and  a  hydrogen  atom  respectively  in  union  with  two  carbon  atoms 
directly  linked  together. 

Other  examples  serve  as  further  illustrations  of  this  principle.   If 

'  pTT 

HI  be  removed  from  a  pentyl  iodide,  n  Tj3>CH-CH2[,  the  result- 

U2rl5 

ing  amylene,  C5H10,  should,  in  accordance  with  the  principle,  have 

prr 

the  constitution  n  vr3>C-CH2.     That  it  actually  has  is  proved  bv 
^2*15      |    | 

the  fact  that  the  addition-product  obtained  by  the  action  of  h^ydri- 
odic  acid  on  this  amylene  is  not  the  original  pentyl  iodide,  but  one 


154  ORGANIC  CHEMISTRY.  [§  119 

with  the  formula  n  TT3>CI-CH3,  as  is  established  by  replacement 


of  I  by  OH,  and  comparison  of  the  tertiary  alcohol  thus  obtained 
with  that  of  the  same  formula  prepared  by  the  synthetic  method 
described  in  102. 

The  constitution  of  another  pentyl  iodide,  (CH3)2CH  -CH2  -CH2I, 
which  yields  CsH^o  on  elimination  of  HI,  may  be  similarly  estab- 
lished. With  hydriodic  acid  this  amylene  yields  another  pentyi 
iodide,  (CH3)2CH'CHI-CH3:  the  constitution  of  this  compound  is 
proved  by  its  conversion  into  an  alcohol  which  yields  a  ketone  on 
oxidation,  and  is  therefore  a  secondary  alcohol. 

BUTLEROW  has  proved  that  the  removal  of  hydrogen  halide  is 
impossible  when  the  halogen  atom  and  hydrogen  atom  are  not 
united  with  carbon  atoms  in  juxtaposition  to  one  another.  He 
converted  tsobutylene,  (CH3)2C:CH2,  by  addition  of  two  bromine 
atoms  into  (CH3)2CBr-CH2Br.  Elimination  of  HBr  from  this  di- 
bromide  produced  (CH»)2C  :CHBr,  the  constitution  of  which  is  in- 
ferred from  its  oxidation  to  acetone  : 

(CH3)2C|:CHBr  ->  (CH3)2CO. 

It  was  not  possible  again  to  eliminate  HBr  from  the  compound 
(CH3)2C:CHBr,  monobromobutylene,  there  being  no  hydrogen  at- 
tached to  the  carbon  atom  in  direct  union  with  the  CHBr-group. 

119.  From  the  foregoing  considerations  it  is  evident  that  only 
three  possible  constitutional  formulae  remain  for  the  unsaturated 
hydrocarbons. 

1.  Two  free  bonds  on  two  carbon  atoms  directly  linked  to  one 
another:  R-CH-CH-R'. 

I        I 

ni      in 

2.  Tervalent  carbon  atoins  in  direct  union:  R'CH-CH»R'. 

3.  A  double  bond  between  two  carbon  atoms:  R-CH:CH«R'. 
For  several  reasons  the  preference  is  given  to  the  formula  with 

the  double  bond.  First,  it  would  be  remarkable  if  only  carbon 
atoms  in  juxtaposition  to  one  another  could  have  free  bonds,  or  be 
tervalent.  Second,  experience  has  shown  that  unsaturated  com- 
pounds containing  an  uneven  number  of  free  bonds  or  tervalent 
carbon  atoms  do  not  exist.  Next  to  the  saturated  hydrocarbons 


§  120J        THE  NATURE  OF  THE  DOUBLE  CARBON  BOND.         155 

CnH2n_j_2;  come  in  order  of  the  number  of  hydrogen  atoms,  GuH^nt 
CnH2ri-2,  etc.  Hydrocarbons,  GnH2lJ4.i,  CnH2n_1,  etc.,  with  one  or 
three  free  bonds,  or  tervalent  carbon  atoms,  are  unknown,  all 
attempts  to  isolate  methyl  CH3,  ethyl  C2H5,  etc.,  having  failed.  The 
facts  afford  no  support  for  the  assumption  of  either  free  bonds  or 
of  tervalent  carbon  atoms.  On  the  other  hand,  in  forming  a  double 
linking  hydrogen  halide  must  be  eliminated  from  adjoining  carbon 
-atoms  in  direct  union,  thus  excluding  the  possibility  of  the  forma- 
tion of  such  compounds  as.  C,1H2n.fl.  Only  the  existence  of  the 
double  bond,  therefore,  explains  the  observed  facts. 

The  non-existence  of  free  bonds  in  the  unsaturated  hydro- 
carbons has  led  by  analogy  to  the  conclusion  that  they  are  also 
absent  irom  other  compounds  containing  atoms  doubly  linked, 
trebly  linked,  etc.,  such  as  nitrogen  in  the  nitriles,  oxygen  in  the 
Icetones,  and  so  on. 

1 20.  The  assumption  of  the  existence  of  multiple  bonds  pre- 
sents at  first  sight,  however,  certain  difficulties  when  the  power 
of  forming  addition-products  possessed  by  all  such  compounds  is 
considered.  As  has  been  stated  several  times,  carbon  bonds  are 
only  severed  with  difficulty  (36),  but  the  double  carbon  bond  is 
very  readily  converted  into  a  single  one  by  formation  of  an  addi- 
tion-product. It  is  still  more  remarkable  that  when  a  substance 
containing  a  double  carbon  bond  is  oxidized,  the  chain  is  always 
severed  at  the  double  bond.  A  satisfactory  explanation  is  afforded 
by  the  fact  that  when  substances  containing  a  double  carbon  bond 
are  oxidized,  it  is  often  possible  to  prove  that  there  is  no  direct 
rupture  of  the  carbon  chain  at  the  double  bond,  but  that  an  addi- 
tion-product is  first  formed  by  the  taking  up  of  two  OH-groups: 

\3H  \CHOH 

becomes 
!H  /CHOH 


Such  derivatives  can  often  be  isolated.  Since  oxidation  always 
takes  place  at  a  point  where  it  has  already  begun  (45),  it  follows 
that  further  oxidation  of  such  a  compound  must  result  in  a  sever- 
ance of  the  carbon  chain  at  the  position  previously  occupied  by  the 
double  bond.  The  breaking  of  the  unsaturated  chain  by  oxidation 
therefore  depends  on  the  formation  of  an  intermediate  addition- 


156  ORGANIC  CHEMISTRY.  [§  120 

product,  and  it  is  only  necessary  to  find  an  explanation  for  the- 
ease  with  which  the  addition  is  effected;  an  object  best  attained  by 
a  consideration  of  the  nature  of  the  bonds  between  the  atoms.  An 
affinity  or  bond  may  be  looked  upon  as  an  attraction  exercised  by 
one  atom  upon  another.  Should  an  atom  possess  more  than  one 
affinity,  it  is  assumed  that  the  attraction  is  exercised  in  more  than 
one  direction,  and  is  concentrated  at  certain  points  of  its  surface, 
somewhat  after  the  manner  in  which  the  attraction  exercised  by  a 
magnet  is  concentrated  at  its  two  poles.  Any  other  assumption, 
such  as  that  the  attracting  force  is  equally  distributed  over  the 
\vhole  surface  of  an  atom,  would  make  it  difficult  to  understand 
how  each  element  could  have  a  determinate  valency.  If  the  carbon 
atom  is  quadrivalent,  there  must  be  on  its  surface  foui  such  points 
or  "poles,"  situated  at  the  angles  of  a  regular  tetrahedron  (48). 
When  there  is  a  single  bond  between  two  such  poles  on  different 
carbon  atoms,  their  mutual  attraction  causes  the  atoms  to  approach 
one  another  as  closely  as  possible. 

VON  BAEYER  has  suggested  that  these  poles  on  the  surface  of 
carbon  atoms  are  movable.  Such  a  movement  results,  however, 
in  a  certain  "  strain/'  and  this  tends  to  make  the  poles  revert  to 
their  original  position.  Thus,  on  conversion  of  a  single  bond 
between  two  carbon  atoms  into  a  double  bond,  the  directions  of 
the  affinities  of  each  carbon  atom  must  undergo  an  appreciable 
alteration: 

—  C  -  C  —    becomes     —  C  —  —  C  —  . 


The  resulting  strain  is  therefore  a  cause  of  the  readiness  with 
which  double  bonds  can  be  severed.  VON  BAEYER'S  strain 
theory  affords  an  explanation  of  other  important  phenomena 
also. 

Evidently  the  double  bond  must  not  be  regarded  as  a  mere 
duplication  of  the  single  bond,  as  the  expression  "double  bond  " 
would  indicate. 

The  presence  of  a  double  bond  exerts  a  great  influence  on 
chemical  properties,  as  has  been  demonstrated,  but  its  effect 
on  physical  properties  is  no  less  marked.  This  phenomenon 
has  been  most  fully  investigated  in  connection  with  refraction.- 


§§121,122]    THE  NATURE  OF  THE  DOUBLE  CARBON  BOND.  157 

The  members  of  a  homologous  series  exhibit  a  constant  dif- 
ference in  molecular  refraction  (26)  for  each  additional  CH2- 
group,  and  this  difference  can  be  regarded  as  the  refraction  of 
this  group.  Multiplying  this  difference  by  n,  and  subtracting 
the  product  from  the  molecular  refraction  of  a  compound  CnH2rH_2, 
give  the  refraction  for  2H,  and  therefore  also  for  C  and  H  separately. 
The  atomic  refraction  of  oxygen  and  other  elements  can  be 
similarly  ascertained.  Inversely,  knowing  the  molecular  formula, 
simple  addition  of  the  atomic  refractions  gives  the  molecular 
refraction,  the  values  calculated  agreeing  well  with  those  deter- 
mined experimentally.  For  an  unsaturated  compound,  however, 
the  molecular  refraction  thus  calculated  is  always  less  by  a  con- 
stant amount  than  that  determined  experimentally.  BRUHL  calls 
this  difference  the  increment  for  the  double  bond.  On  these 
facts  is  based  an  optical  method  of  detecting  the  presence  of 
a  double  carbon  linking  in  a  compound. 

II.  ALICYCLIC  COMPOUNDS,  CnH2n. 

121.  Isomeric  with  the  defines  is  a  series  of  compounds,  CnH2nr 
chiefly  distinguished  from  the  former  by  the  absence  of,  or  at 
least  a  diminution  in,  the  power  of  forming  addition-products. 
Most   of  these   compounds  are   very  stable:    thus  q/c/opentane, 
C5Hi0,  closely  resembles  n-pentane,  C5Hi2.     The  methods  for  the 
formation  of  these  compounds  make  it  evident  that  there  is  a. 
ring  or  closed  carbon  chain  in  the  molecule  (275-280) . 

III.  HYDROCARBONS,  CnH2n-2. 

122.  Two  structures  are  possible  for  these  compounds,  which 
contain  four  hydrogen  atoms  less  than  the  corresponding  paraffins. 
Hydrocarbons  with  two  double  bonds  have  the  general  formula 
CnH2n-25  for  example, 

CH2:CH-CH:CH2. 

Vinylethylene 

Further,  substances  with  a  triple  bond  have  the  same  general  for- 
mula; for  example, 

CH3-C=CH. 

Allylene 


158  ORGANIC  CHEMISTRY  [§  123 

The  triple  linking  here  is  assumed  for  reasons  similar  to  those 
applicable  to  the  double  bond  in  the  defines  (up). 


A.    HYDROCARBONS  WITH  TRIPLE  BONDS. 

Nomenclature. 

123.  The  first  member,  C2H2,  is  called  acetylene:  the  second, 
allylene:  the  higher  members  are  regarded  as  substituted 
acetylenes;  thus  C4H6  is  called  ethylacetylene;  C6H10,  butylacetylene; 
and  so  on. 

Methods  of  Formation. 

1.  By  the  dry  distillation  of  complex  compounds  such  as  coal; 
hence  the  occurrence  of  acetylene  in  coal-gas. 

2.  By  the  withdrawal  of  two  molecules  of  hydrogen  halide  from 
compounds  of  the  formula  CnH2nX2,  where  X  represents  a  halogen 
atom,  these  compounds  having  been  previously  formed  by  the 
addition  of  halogen  to  alkylenes: 

CH2Br— CH2Br  -  2HBr = CH=CH. 

Ethylene  bromide  Acetylene 

The  elimination  of  hydrogen  halide  is  effected  by  heating  with 
alcoholic  potash. 

A  general  method  for  the  preparation  of  unsaturated  com- 
pounds is  furnished  by  this  method  of  adding  on  halogen,  followed 
by  the  removal  of  hydrogen  halide.  Thus  from  CnH2n+2,  CnH2n+1X 
is  obtained  by  the  action  of  chlorine  or  bromine.  Heating  with 
alcoholic  potash  converts  this  into  CnH2n,  from  which  CnH2nBr2 
is  got  by  the  action  of  bromine,  and  is  converted  into  CnH2n_2  by 
abstraction  of  2HBr.  This  compound  can  again  form  an  addition- 
product  with  bromine,  and  so  on. 

3.  By  the  elimination  of  2HX  from  compounds  of  the  formula 
CnH2nX2.  previously  formed  by  the  action  of  phosphorus  penta- 
halide  upon  aldehydes  or  ketones: 

CH3.CHC12  -  2HCI  =  CH^CH. 

Ethylidene  chloride  Acetylene 

CH3.CC12.CH3  -  2HC1  =  CH 

Chloroacetone  Allylene 


§§  124,  125]       HYDROCARBONS  WITH  TRIPLE  BONDS.  159 

124.  Some  of  the  hydrocarbons  prepared  by  the  foregoing 
methods  exhibit  a  characteristic  behaviour  towards  an  ammoniacal 
solution  of  cuprous  chloride  or  of  a  silver  salt,  which  affords  a  ready 
means  of  recognizing  them.  By  replacement  of  hydrogen,  they  yield 
metallic  derivatives,  insoluble  in  the  ammoniacal  solution  or  in 
water,  which  separate  out  as  a  voluminous  precipitate.  These 
compounds  are  explosive,  the  copper  yellow  or  red,  and  the  silver 
white.  Acetylene,  and  of  its  higher  homologues,  those  derived 
from  the  dihalogen  compounds  of  the  aldehydes,  yield  these  metallic 
compounds.  The  method  of  formation  of  these  homologues  shows 
that  they  contain  the  group  =CH  : 

CnH2n+1  -CH2  -CHO  ->  CnH2n+i  -CH2  -CHC12  -»  CnH2n+1  -C=CH. 

From  this  it  may  be  concluded  that  the  presence  of  the  group  EECH 
is  essential  to  the  yielding  of  metallic  derivatives:  it  is  the  hydrogen 
of  this  group  which  is  replaced  by  metals.  In  support  of  this  view 
is  the  fact  that  only  the  dichloro-derivatives  of  the  methylketones 
(101)  can  be  transformed  into  hydrocarbons  yielding  metallic 
compounds: 


Yields  metallic  derivatives 

C2H5.CO.C2H5-,C2H5.CC12.CH2.CH3^C2H5.C=C.CH3. 

Does  not  yield  metallic 
derivatives 

The  isomeric  hydrocarbons  containing  two  double  bonds  (127)  are 
also  incapable  of  forming  metallic  compounds. 

The  hydrocarbons  are  readily  liberated  from  their  metallic 
derivatives  by  the  action  of  dilute  hydrochloric  acid.  This  affords 
a  means  of  isolating  from  mixtures  the  members  of  the  series 
CnH2n-2  which  yield  such  derivatives,  and  of  obtaining  them  in 
the  pure  state. 

125.  The  hydrocarbons  of  this  series  can  add  on  four  halogen 
atoms  or  two  molecules  of  a  hydrogen  halide.  In  presence  of 
mercury  salts  they  can  take  up  water,  forming  aldehydes  or  ketones  : 

CH=CH  +  H20  =  CH3'CHO. 

=CH3.CO-CH3. 


Mercury   compounds  are  first   formed  by   addition:    thus,   when 
allylene,  C3H4,  is  passed  into  a  solution  of  mercuric  chloride,  there 


160  ORGANIC  CHEMISTRY.  [§  126 

is  first  formed  a  precipitate  of  the  composition  3HgCl2,3HgO,2C3H4, 
which  is  converted  into  acetone  by  the  action  of  hydrochloric 
acid. 

The  hydrocarbons  of  the  acetylene  series  also  yield  condensa- 
tion-products. The  condensation  sometimes  takes  place  between 
three  molecules:  thus,  acetylene,  C2H2,  condenses  to  benzene, 
CeHe;  dimethylacetylene,  C±HG,  to  hexamethylbenzene,  C12H18; 
etc.  This  transformation  is  effected  by  the  action  of  heat  on  acety- 
lene, and  of  sulphuric  acid  on  its  homologues. 

A  remarkable  reaction,  resulting  in  a  change  in  the  position  of 
the  triple  bond,  takes  place  when  the  hydrocarbons  of  the  series 
CnH2n_2  containing  the  group  =CH  are  heated  to  a  high  tempera- 
ture in  a  sealed  tube  with  alcoholic  potash: 

C2H5-CH2.C=CH  is  converted  into  C2H5.C=C.CH3. 

Propylacetylene  Methylethylacetylene 

It  is  probable  that  addition  at  one  part  of  the  molecule  is  followed 
by  the  elimination  of  atoms  from  another  part.  The  displacement 
of  the  triple  linking  in  the  instance  cited  is  proved  by  the  fact  that 
although  propylacetylene  yields  metallic  derivatives,  the  substance 
obtained  by  heating  it  with  alcoholic  potash  does  not,  but  is  con- 
verted by  oxidation  into  propionic  acid  and  acetic  acid.  This  deter- 
mines the  position  of  the  triple  bond,  since,  for  reasons  similar  to 
those  applicable  to  the  double  bond  (120),  the  carbon  chain  is 
broken  by  oxidation  at  the  point  occupied  by  the  multiple  bond. 
The  substance  obtained  must  therefore  have  the  formula  given 
above,  and  be  methylethylacetylene. 

Acetylene,  C2H2. 

126.  Acetylene  is  a  colourless  gas  of  disagreeable  odour,  is 
somewhat  soluble  in  water,  and  condenses  at  18°  and  83  atmos- 
pheres to  a  liquid  boiling  at  —82-4°.  It  can  be  synthesized  from 
its  elements  by  the  aid  of  an  electric-arc  discharge  between  carbon 
poles  in  an  atmosphere  of  hydrogen,  but  the  maximum  yield  of" 
acetylene  at  2500°  is  only  3-  7  per  cent.  At  the  same  temperature, 
about  1-2  per  cent,  of  methane  and  a  trace  of  ethane  are  simul- 
taneously formed.  The  presence  of  acetylene  can  be  detected 
by  means  of  an  ammoniacal  solution  of  cuprous  chloride,. 


§  126]  HYDROCARBONS  WITH  TRIPLE  BONDS.  161 

which  yields  a  red  precipitate  of  copper  acetylene  even  from 
traces  of  acetylene  mixed  with  other  gases.  Acetylene  is  also 
obtained  as  a  product  of  the  incomplete  combustion  of  many 
organic  substances.  It  is  prepared  on  the  large  scale  by  the  action 
of  water  on  calcium  carbide,  or  calcium  acetylene,  CaC2 : 

CaC2  +  2H2O  =  Ca(OH)2  +  C2H2. 

The  reaction  is  somewhat  violent,  and  is  attended  with  the  evolu- 
tion of  a  considerable  quantity  of  heat.  Calcium  carbide  is  pre- 
pared by  heating  carbon  with  quicklime,  CaO,  in  an  electric  furnace. 
Under  the  influence  of  the  high  temperature,  the  calcium  liberated 
by  the  action  of  the  carbon  on  the  quicklime  enters  into  combina- 
tion with  the  excess  of  carbon,  forming  calcium  carbide:  when 
pure,  it  is  white,  but  has  usually  a  dark  reddish-brown  colour,  due 
to  the  presence  of  small  quantities  of  iron. 

Various  applications  of  acetylene  have  been  facilitated  by  the 
cheap  and  simple  method  available  for  its  preparation  from  cal- 
cium carbide.  A  solution  in  acetone  is  usually  employed  in  the 
arts  and  manufactures,  the  gas  being  compressed  at  twelve  atmos- 
pheres into  steel  cylinders  containing  this  solvent.  At  this  pressure, 
one  volume  of  acetone  dissolves  about  three  hundred  volumes  of 
acetylene.  When  the  gas  evolved  from  this  solution  is  allowed  to 
issue  from  a  fine  orifice  and  ignited,  it  burns  with  a  smokeless,  bright 
luminous  flame,  and  is  employed  as  an  illuminant  in  railway-car- 
riages, motor-car  lamps,  gas-buoys,  and  so  on.  Another  important 
application  is  exemplified  by  autogenous  welding,  sufficient  heat 
being  generated  by  an  oxy-acetylene  blowpipe  to  melt  iron  readily. 
Steel  plates  for  safes,  rails  for  railway  or  tramway  use,  and  other 
iron  or  steel  material  can  be  readily  welded  by  its  aid. 

Acetylene  must  be  handled  carefully,  since  a  mixture  with  air 
explodes  with  extreme  violence,  and  is  much  more  dangerous  than 
a  mixture  of  ordinary  coal-gas  and  air.  This  is  due  to  the  fact 
that  much  heat  is  taken  up  in  the  formation  of  acetylene:  it  is 
strongly  endothermic  ("Inorganic  Chemistry,"  97).  Moreover, 
the  limits  of  explosion  are  much  wider  than  for  any  other  gas,  an 
explosive  mixture  being  formed  with  air  by  the  admixture  of 
3-82  per  cent,  of  acetylene,  while  for  coal-gas  the  limits  are  only 
5-28  per  cent.  The  velocity  of  propagation  of  combustion  is  also 
much  greater  for  acetylene,  and  this  augments  considerably  the 
force  of  the  explosion. 


162  ORGANIC  CHEMISTRY.  [§  127' 

Acetylene  prepared  from  calcium  carbide  sometimes  contains 
small  quantities  of  hydrogen  sulphide  and  phosphine,  to  which  it 
owes  its  disagreeable  odour.  It  can  be  freed  from  the  former  by  a 
solution  of  caustic  alkali,  and  from  the  latter  by  a  solution  of 
mercuric  chloride  in  hydrochloric  acid.  The  removal  of  phosphine 
is  of  special  importance,  since  its  presence  may  lead  to  the  spon- 
taneous ignition  of  the  gas. 


B.  HYDROCARBONS  WITH  TWO  DOUBLE  BONDS. 

127.  A  hydrocarbon  of  this  series  of  great  importance  is  isoprene, 
C5H8,  on  account  of  its  close  relationship  to  caoutchouc  (370).  In 
recent  years  many  attempts  to  prepare  isoprene  have  been  made, 
but  hitherto  without  technical  success.  A  very  good  laboratory- 
method  for  its  preparation  is  described  in  367.  A  poor  yield  of  the 
hydrocarbon  is  obtained  by  the  dry  distillation  of  caoutchouc.  It 
is  a  liquid  boiling  at  37°,  and  has  the  specific  gravity  D421  =0*6793. 

C^TT 

Isoprene  is  proved  to  have  the  constitution  r>TJ2^C*  CH=CH2  by  the 

Oils 
/~1TT 

addition  of  2HBr.  which  yields  a  dibromide.  ^;;3>CBr—  CH2—  CH2Br. 

Oils 

OTT 

identical  with  that  obtained  from  dimethylallene,  /-,TT3>  C=G=CH2. 

U.H.3 
Dimethylallene    is    thus    obtained.      Two    carbinol-derivatives, 

pTT 

dimethylethylcarbinol,     ^g3>C(OH)  .CH2-CH3,  and  methyhsopro- 
pylcarbinol,  {^3>CH.CHOH.CH3,  are  prepared    by  the  method 

described  in   102,   and  converted  into  the   corresponding  iodides. 
On    elimination    of     HI,    each    iodide    yields    trimethylethylene, 

pTT 

Qjj^C^CH'CHg,  its  formation  from  both  iodides  admitting  of  no 
other  position  for  the  double  bond.     Trimethylethylene  takes  up 

pTT 

2Br,  forming  ^g3>CBr-CHBr.CH3.      On   treatment  of  this  sub- 

stance with  alcoholic  potash,  two  molecules  of  hydrobromic  acid, 
2HBr,    are    eliminated,    with    the    formation    of    dimethylallene, 

*~ 


This  mode  of  formation  does  not  wholly  preclude  another 
arrangement  of  the  double  bonds,  but  other  evidence  proves  that 
dimethylallene  has  the  structural  formula  indicated: 

1.  On  oxidation  it  yields  acetone,  proving  the  presence  of  the 
group  (CH,)2C=. 


§  127]  HYDROCARBONS   WITH  TWO  DOUBLE  BONDS.          1G3 

2.  Treatment  with  sulphuric  acid  of  50  per  cent,  strength  con- 
verts it  into  methyl?  sopropylketone: 


Intermediate  product 


Compounds  like  this  intermediate  product  are  referred  to  in  149. 

When  forming  an  addition-product  with  two  univalent  atoms, 
organic  compounds  containing  the  group  C=C  —  C—  C,  called  by 
THIELE  a  "  Conjugated  system,"  often  behave  peculiarly,  the 
addition  taking  place  at  C-atoms  1  and  4,  with  formation  of  a 
double  bond  between  C-atoms  2  and  3: 


=  CH2Br.CH=CH.CH2Br. 

The  subject  of  conjugated  bonds  is  further  discussed  in  283. 


SUBSTITUTION-PRODUCTS   OF  THE   UNSATURATED 
HYDROCARBONS. 


I.  UNSATURATED   HALOGEN  COMPOUNDS. 

128.  Since  the  saturated  hydrocarbons  do  not  themselves  pos- 
sess any  salient  characteristics,  the  properties  of  their  compounds 
•depend  upon  the  nature  of  the  substituents.  Hitherto,  only  com- 
pounds with  properties  due  to  the  presence  in  the  molecule  of  a 
single  group,  such  as  hydroxyl,  carboxyl,  a  multiple  carbon  bond, 
etc.,  have  been  described.  Substances  containing  more  than  one 
characteristic  group  in  the  molecule  must  now  be  considered. 

When  these  groups  are  present  simultaneously  in  the  same 
molecule,  they  exercise  a  modifying  influence  upon  one  another. 
The  extent  of  this  influence  varies  considerably,  as  is  evident  from 
-a  consideration  of  the  different  classes  of  unsaturated  halogen 
compounds. 

Halogen  derivatives  of  the  type  CnH2n-iX  are  obtained  by  the 
addition  of  halogen  to  the  hydrocarbons  CnH2n,  and  subsequent 
elimination  of  one  molecule  of  hydrogen  halide: 

CH2r=CH2  +  Br2  =  CH2Br—  CH2Br. 
CH2Br-CH2Br-HBr  =  CH2—  CHBr. 

Ethylene  bromide  Vinyl  bromide 

They  are  also  formed  by  removal  of  one  molecule  of  hydrogen 
halide  from  compounds  containing  two  halogen  atoms  in  union 
with  the  same  carbon  atom: 


CH3.CH2.OKC12-HCL  =  CH 

Propylidene  chloride  a-Chloropropylene 

CH3.CC12.CH3-HC1  =  CH3-CC1=:CH2. 

Cbloroacetone  fl-Chloropropylene 

164 


§129]  UNSATURATED  HALOGEN  COMPOUNDS.  165 

The  methods  employed  in  the  preparation  of  these  compounds 
indicate  that  their  halogen  atom  is  in  union  with  a  carbon  atom 
having  a  double  bond.  Their  properties  differ  widely  from  those 
of  compounds  like  the  alkyl  halides,  with  the  halogen  atom  attached 
to  a  singly-linked  carbon  atom;  and  this  rule  is  general  for  such 
compounds.  Ths  halogen  atom  of  the  alkyl  halides  is  especially 
able  to  take  part  in  double  decompositions:  it  is  replaceable  by 
hydroxyl,  an  alkoxyl-group,  an  acid-residue,  the  amino-group,  and. 
so  on. 

This  aptitude  for  double  decomposition  is  almost  lacking  in  com- 
pounds with  halogen  in  union  with  a  doubly-linked  carbon  atom* 
Alkalis  do  not  convert  them  into  alcohols,  nor  alkoxides  into  ethers: 
but  invariably,  when  they  do  react,  hydrogen  halide  is  eliminated,, 
with  formation  of  hydrocarbons  of  the  series  CnH2n_2. 

129.  An  isomeride  of  a-chloropropylene  and  ft-chloropropylene, 
which  have  been  referred  to  above,  is  called  allyl  chloride.  Its 
halogen  atom  takes  part  in  double  decompositions  as  raadily  as 
the  halogen  atom  of  an  alkyl  chloride.  Allyl  chloride  is  obtained 
by  the  action  of  phosphorus  pentachloride  upon  allyl  alcohol, 
prepared  by  a  method  described  in  153.  This  alcohol  yields 
n-propyl  alcohol  by  addition  of  hydrogen,  and  its  hydroxyl- 
group  must  therefore  be  at  the  end  of  the  carbon  chain.  Hence, 
the  halogen  atom  in  allyl  chloride  must  also  be  at  the  end  of  the 
chain,  since  it  takes  the  place  of  the  hydroxyl-group.  Given  the 
constitutions  of  a-propylene  chloride  and  /?-propylene  chloride, 
which  are  deduced  from  those  of  propionaldehyde  and  acetone,  the 
allyl  halides  can  only  have  the  constitutional  formula 

CH2=CH.CH2X. 

The  halogen  atom  is  attached  to  a  singly-linked  carbon  atom,  and 
retains  its  normal  character  despite  the  presence  of  a  double  bond 
in  the  molecule. 

The  influence  exerted  upon  the  character  of  a  halogen  atom  by 
its  position  in  the  molecule  of  an  unsaturated  compound  affords  a 
means  of  determining  whether  it  is  attached  to  a  singly-linked  or 
doubly-linked  carbon  atom,  the  indication  being  its  possession  or 
lack  of  the  power  to  take  part  in  double  decompositions. 

The  following  are  examples  of  individual  members  of  the  series. 
Vinyl  chloride  CH2:CHC1  is  a  gas,  vinyl  bromide  CH2:CHBr  a 


166  ORGANIC  CHEMISTRY.  [§§  130,  131 

liquid  of  ethereal  odour.  Both  these  compounds  polymerize 
readily. 

130.  Allyl  chloride,  allyl  bromide,  and  allyl  iodide,  boil  respec- 
tively at  46°,  70°,  and  103°.     They  are  often  employed  in  syntheses 
to  introduce  an  unsaturated  group  into  a  compound.     They  have  a 
characteristic  odour  resembling  that  of  mustard. 

The  propargyl  compounds,  CHEEOCH2X,  are  a  type  of  the 
series  CnH2n_3X.  Their  constitution  is  inferred  from  the  facts 
that  they  yield  metallic  derivatives,  indicating  the  presence  of  the 
group  ^CH,  and  that  their  halogen  atoms  are  capable  of  taking 
part  in  double  decompositions,  proving  their  union  with  a  singly- 
linked  carbon  atom.  They  are  obtained  from  propargyl  alcohol 
(133)  by  the  action  of  phosphorus  pentahalides,  and  are  liquids  of 
pungent  odour. 

Bromoacetylidene,  CHBr:C,  which  is  assumed  by  NEF  to  contain 
a  bivalent  carbon  atom,  can  be  obtained  from  acetylene  bromide, 
CHBnCHBr,  by  treatment  with  alcoholic  potash.  It  is  a  gas, 
boils  at  —2°,  and  takes  fire  spontaneously  in  the  air.  Its  solution  in 
alcohol  is  phosphorescent,  owing  to  slow  oxidation,  and  the  gas  itself 
has  an  odour  very  similar  to  that  of  phosphorus. 

II.  UNSATURATED  ALCOHOLS. 

131.  The  hydroxyl-group  of  the  unsaturated  alcohols  may  be 
attached  to  a  singly-linked  or  to  a  doubly-linked  carbon  atom: 

CH2 :  CH  •  CH2OH,        CH2 :  CH  •  OH. 

Allyl  alcohol  Vinyl  alcohol 

Few  compounds  of  the  type  of  vinyl  alcohol  are  known.  It  is  found 
that  reactions  which  might  be  expected  to  yield  them  generally 
result  in  the  formation  of  their  isomerides.  Thus,  when  water  is 
abstracted  from  glycol,  CH2OH«CH2OH,  there  results,  not  vinyl 

TT    • 

alcohol,  CH2— CHOH,  but  an  isomeride,  acetaldehyde,  CH3 — C^  Q. 

When  /?-bromopropylene,  CH3-CBr:CH2,  is  heated  with  water, 
there  is  formed  not  /?-hydroxypropylene,  CH3»C(OH)  :CH2,  but 
the  isomeric  acetone,  CH3 •  CO •  CH3.  The  rule  is  that  when  a  group- 
ing of  the  atoms  in  the  form  — CH:C(OH) —  would  be  expected,  a 
transformation  into  — CH2-CO —  usually  occurs.  Although  most 
substances  containing  hydroxyl  attached  to  a  doubly-linked  carbon 


§132]  UNSATURATED  ALCOHOLS.  167 

atom  are  unstable,  they  have  a  tendency  to  become  transformed 
into  isomerides.  Compounds  do  exist,  however,  in  which  the 
group  — CH:C(OH)—  is  stable  (235-236). 

The  following  compounds  either  contain  hydroxyl  in  union  with 
a  doubly-linked  carbon  atom,  or  are  related  to  substances  of  that 
type. 

Vinyl  alcohol,  CH2:CHOH,  so  called  because  it  contains  the 
vinyl-group,  CH2:CIi — ,  is  probably  present  in  ordinary  ethyl  ether 
owing  to  partial  oxidation.  When  such  ether  is  agitated  with  an 
alkaline  solution  of  a  mercury  salt,  a  precipitate  of  the  composition 
Hg3Cl2O2C2H3  is  formed,  and  on  treatment  with  hydrogen  halide 
yields  vinyl-compounds. 

A  vinyl-derivative  of  great  physiological  importance,  called  neu- 
rine,  is  formed  in  the  putrefactive  decay  of  flesh,  and  in  other  fer- 
mentation-processes. Its  constitution  is  (CH3)3N<QTr  2,  as  is 

indicated  by  synthesis.  When  trimethylamine  reacts  with  ethy- 
lene  bromide,  a  substituted  ammonium  bromide  of  the  formula 

(CH3)3N<™2*CH2Br  is  obtained.     HBr  is  eliminated  from   the 

group  — CH2-CH2Br  by  the  action  of  moist  silver  oxide,  the  bromine 
atom  attached  to  nitrogen  being  simultaneously  replaced  by  hy- 
droxyl. A  substance  of  the  constitution  indicated  is  thus  obtained, 
and  is  in  all  respects  similar  to  neurine. 

Allyl  Alcohol,  CH2:CH-CH2OH. 

132.  Many  unsaturated  alcohols  containing  hydroxyl  attached 
to  a  singly-linked  carbon  atom  are  known.  The  most  important 
is  all'jl  alcohol,  the  preparation  of  which  is  described  in  153.  Its 
constitution  is  inferred  from  that  of  the  chlorine  derivative  formed 
by  the  action  of  phosphorus  pentachloride  (129) ;  as  well  as  from 
that  of  the  products  obtained  by  oxidation,  by  which  allyl  alcohol  is 
converted  first  into  an  aldehyde,  acraldehyde,  and  then  into  acrylic 
add: 


Allyl  alcohol  Acraldehyde  Acrylic  acid 

Allyl  alcohol  must  therefore  contain  the  group  — CH2OH,  charac- 
teristic of  primary  alcohols. 


168  ORGANIC  CHEMISTRY.  [§  133 

Allyl  alcohol  is  a  liquid  of  irritating  odour,  solidifying  at  —50°, 
and  boiling  at  96-5°,  and  is  miscible  with  water  in  all  proportions. 
Its  specific  gravity  at  0°  is  0-872.  It  forms  addition-products  with 
the  halogens  and  with  hydrogen,  with  the  latter  yielding  n-propyl 
alcohol. 

Many  other  compounds  containing  the  allyl-group,  CH2 :  CH  'CH2 — , 
are  known,  among  them  allyl  sulphide  (CH,:CH'CH.,)2S,  the  prin- 
cipal constituent  of  oil  of  garlic.  It  is  synthetically  obtained  by 
the  action  of  potassium  sulphide,  K2S,  on  allyl  iodide. 

It  is  apparent  that  the  influence  of  the  double  bond  in  the 
unsaturated  halogen  compounds  and  alcohols  is  very  pronounced 
when  it  is  situated  in  the  immediate  neighbourhood  of  halogen  or 
hydro xyl,  but  that  otherwise  its  influence  is  much  less  marked. 
When  two  groups  are  situated  in  immediate  proximity  to  one  another 
in  the  same  molecule,  each  group  exercises  a  strong  influence  upon  the 
properties  oj  the  other. 

Propargyl  Alcohol,  CH=C-CH2OH. 

133.  Propargyl  alcohol  contains  a  triple  bond,  and  is  prepared  from 
tribromohydrin,  CH2Br  •  CHBr  •  CH2Br  (147) .  Potassium  hydroxide 
converts  this  substance  into  CH2:CBr«CH2Br,  which  on  treatment 
with  potassium  acetate  and  saponification  yields  CH2:  CBr-  CH2OH, 
since  only  the  terminal  Br-atom  is  capable  of  taking  part  in  a  double 
decomposition  (128).  When  this  alcohol  is  again  brought  into  con- 
tact with  caustic  potash,  HBr  is  eliminated,  with  formation  of  pro- 
pargyl  alcohol,  the  constitution  of  which  is  indicated  by  this  method 
of  formation  and  also  by  its  properties.  The  presence  of  the  group 
=CH  is  indicated  by  the  formation  of  metallic  derivatives:  on 
oxidation  it  yields  propiolic  acid,  CH^C'COOH,  with  the  same 
number  of  carbon  atoms,  proving  that  it  is  a  primary  alcohol. 

Propargyl  alcohol  is  a  liquid  of  agreeable  odour,  soluble  in  water, 
and  boiling  at  114°-115°:  its  specific  gravity  at  21°  is  0-963.  Its- 
metallic  derivatives  are  explosive. 


MONOBASIC   UNSATURATED   ACIDS. 


I.  ACIDS  OF  THE  OLEIC   SERIES,  CnH2n_202- 

134.  The  acids  of  the  olelc  series  can  be  obtained  from  the 
saturated  acids  CnH2n02  by  the  methods  generally  applicable  to  the 
conversion  of  saturated  into  unsaturated  compounds. 

1.  Substitution  of  one  hydrogen  atom  in  the  alkyl-group  of  a 
saturated  acid  by  a  halogen  atom,  and  subsequent  elimination  of 
hydrogen  halide  by  heating  with  alcoholic  potash. 

2.  Removal  of  the  elements  of  water  from  the  monohydroxy- 
acids  : 


CH3-CHOH.CH2.COOH-H2O 

^-Hydroxy  butyric  acid  Ootonic  acid 

The  acids  of  this  series  can  also  be  prepared  from  unsaturated 
compounds  by 

3.  Oxidation  of  the  unsaturated  alcohols  and  aldehydes. 

4.  The  action  of  potassium  cyanide  on  unsaturated  halogen 
compounds,  such  as  allyl  iodide,  and  hydrolysis  of  the  resulting 
nitrile. 

Nomenclature. 

Most  of  the  acids  of  the  ole'ic  series  are  named  after  the 
substances  from  which  they  were  first  obtained,  but  a  few  of  the 
middle  members  have  names  indicating  the  number  of  carbon 
atoms  in  the  molecule.  The  first  member,  CH2:CIi-COOH,  is 
called  acrylic  acid:  others  are  croionic  acid,  C4H6O2;  angelic  acid 
and  iiglic  acid,  C5H8O2;  undecylenic  acid,  CnH20O2;  olelc  acidf 
Ci8H3402;  erucic  acid,  C22H42O2;  etc. 

169 


170  ORGANIC  CHEMISTRY.  [§§135,136 

Properties. 

135.  In  common  with  all  compounds  containing  a  double  bond,\ 
the  acids  of  this  series  possess  the  power  of  forming  addition- 
products.  They  are  "  stronger  "  acids  thar  the  corresponding  fatty 
acids  containing  the  same  number  of  carbon  atoms  in  the  molecule : 
thus,  the  valuo  of  the  constant  104fc  (87)  for  propionic  acid,  C3H6O2r 
is  0-  134;  for  acrylic  acid,  C3H402,  0-56;  for  butyric  acid,  C4H8O2; 
0-149;  for  crotonic  acid,  C4H6O2,  0-204;  etc.  The  double  bond 
renders  the  acids  of  the  ole'ic  series  much  more  susceptible  to  oxida- 
tion than  those  of  the  fatty  series  (120).  The  former  are  converted 
by  energetic  oxidizers  into  two  saturated  acids,  but  when  the  reac- 
tion is  made  less  energetic  by  using  a  dilute  solution  of  potas- 
sium permanganate,  a  dihydroxy-acid  containing  the  group 
— CHOH-CHOH —  is  formed  as  an  intermediate  product,  and  on 
further  oxidation  the  chain  is  severed  at  the  bond  between  these 
two  carbon  atoms  (120).  This  behaviour  affords  a  means  of  deter- 
mining the  position  of  the  double  bond  in  the  molecule.  A  breaking 
down  of  the  molecule  with  formation  of  saturated  fatty  acids  also 
results  on  fusion  of  an  unsaturated  acid  with  caustic  potash  in 
presence  of  air: 


CnH2n+i-CH: 

KO 

KO 

0 


CH-COOH  OH 

=  CnH2n+1.C|OK+CH3.COOH, 
OK 


Formerly  the  reaction  was  employed  to  determine  the  position  of 
the  double  bond,  on  the  assumption  that  the  division  of  the  mole- 
cule was  effected  at  the  point  where  this  bond  was  situated  in  the 
first  instance.  It  is  now  known  that  under  the  influence  of  fused 
caustic  potash,  or  even  by  boiling  with  a  solution  of  caustic  soda, 
the  position  of  the  double  bond  is  displaced  nearer  that  of  the 
carboxyl-group.  Fusion  with  caustic  potash  cannot,  therefore, 
be  employed  as  a  means  of  determining  the  position  of  double 
bonds.  The  action  of  ozone  on  these  acids  is  described  in  198, 

Acrylic  Acid,  CH2:CH-COOH. 

136.  Acrylic  acid  is  obtained  by  the  elimination  of  HI  from 
/2-iodopropionic  acid,  CH2I-CH2-COOH.  It  is  a  liquid  of  pungent 
odour,  boiling  at  140°,  and  is  reduced  by  nascent  hydrogen  to  pro- 
pionic acid. 


§  136  ACIDS  OF  THE  OLE  1C  SERIES.  171 

Acids  of  the  formula  C4H6O2. 

The  theoretically  possible  acids  of  the  formula  C4H6O2  are 
1.  CH2:CH.CH2.COOH;     2.  CH3.CH:CH.COOH; 

PTT  CH2 

3.  CH2:C<^H;         4.       |      >CH.COOH; 

CH2 

but  five  acids  of  the  formula  C4H6O2  are  known. 

An  acid  of  the  constitution  indicated  in  formula  1,  vinylacetic 
acid,  can  be  obtained  by  the  action  of  carbon  dioxide  on  allyl  mag- 
nesium bromide,  and  decomposition  of  the  primary  product  by 
acidulated  water: 

CH2  :  CH  •  CH2MgBr  +  C02  =  CH2  :  CH  -  CH2  -  CO2MgBr  ; 

CH2  :  CH  -  CH2  -  CO2MgBr  +H2O  - 

=  CH2:CH.CH2.COOH+MgBr.OH. 

Its  formation  by  the  action  of  potassium  cyanide  on  allyl  iodide, 
and  hydrolysis  of  the  nitrile  thus  formed,  might  be  expected: 

CH2:CH.CH2I->CH2:CH.CH2CN->CH2:CH.CH2.COOH. 

Allyl  iodide 

Actually,  however,  an  acid  of  formula  2  is  obtained,  solid  crotonic 
add,  which  melts  at  71°  and  boils  at  180°:  careful  oxidation  with 
permanganate  converts  it  into  oxalic  acid,  HOOC  —  COOH,  a  proof 
of  its  constitution.  It  follows  that  during  the  reaction  the  position 
of  the  double  bond  must  have  changed. 

isoCrotonicacid,  melting  at  15-5°  and  boiling  at  172°,  has  also 
constitution  2,  because,  on  the  one  hand,  like  solid  crotonic  acid 
it  can  be  reduced  to  n  -butyric  acid,  proving  that  it  too  contains 
a  normal  carbon  chain;  on  the  other,  it  is  converted  by  careful 
oxidation  into  oxalic  acid.  Ordinary  constitutional  -formula  are 
incapable,  therefore,  of  accounting  for  the  isomerism  of  these  acids, 
which  is  explained  in  169. 

An  acid  with  formula  3  is  obtained  by  the  elimination  of  HBr 
from  bromoisobutyric  acid;  it  is  called  methacrylic  acid: 


The  acid  of  formula  4  is  described  in  275. 


a  72  ORGANIC  CHEMISTRY.  [§  137 


Oleic  Acid,  Ci8H34O2. 

137.  Oleic  acid  is  obtained  by  the  saponification  of  oils  and 
•soft  fats  (85).  To  separate  it  from  the  saturated  fatty  acids, 
stearic  and  palmitic,  simultaneously  liberated,  the  lead  salt  is  pre- 
pared. Lead  oleate  is  soluble  in  ether,  while  lead  palmitate  and 
stearate  are  not.  The  oleic  acid  is  liberated  from  the  lead  oleate 
by  treatment  with  acids. 

At  ordinary  temperatures,  oleic  acid  is  a  liquid  without  odour 
-and  of  an  oily  nature.  It  melts  at  14°.  It  oxidizes  readily  in  the 
air,  and  cannot  be  distilled  at  ordinary  pressures  without  decom- 
position. 

Oleic  acid  contains  a  normal  carbon  chain,  since  on  reduction 
it  yields  stearic  acid. 

KRAFFT  has  proved  the  normal  structure  of  stearic  acid  by  con- 
verting it  step  by  step  into  acids  with  a  smaller  number  of  carbon 
atoms.  When  submitted  to  dry  distillation  in  a  vacuum,  barium 
stearate  and  barium  acetate  form  a  ketone, 


C17H35'  iCOOba*  +baQ.)OC.CH3  -»  C17H35-CQ.CH3. 

Barium  stearate  Barium  acetate        Margarylmethylketone 

On  oxidation,  this  ketone  yields  acetic  acid  and  an  acid  of  the  for- 
mula C17H34O2.  This  proves  that  the  ketone  contains  a  CH2-group 
next  to  the  carbonyl-group,  and  has  the  formula  C^H^  -CH2  «CO  'CH3, 
for  only  from  such  a  compound  could  oxidation  produce  an  acid 
with  seventeen  carbon  atoms.  This  acid,  C17H34O2  (margaric  acid), 
is  similarly  transformed  into  a  ketone,  CJ6H33»CO'CH3,  which  on 
oxidation  yields  an  acid  Ci6H32O2.  The  formula  of  margaric  acid 
must  therefore  be  C15H31^CH2-COOH.  and  that  of  stearic  acid, 
C15H3,  .CH2.CH2-COOH.  The  acid  C16H32O2,  palmitic  acid,  is  in  its 
turn  converted  into  a  ketone,  and  the  process  continued  until  capric 
acid,  C10H20O2,  is  obtained.  This  acid  has  been  proved  by  synthesis 
(233»  1)  to  contain  a  normal  carbon  chain. . 

The  presence  of  a  double  bond  in  oleic  acid  is  indicated  by  its 
iorming  an  addition-product  with  bromine,  and  by  its  power  of 
reducing  an  alkaline  permanganate  solution  (113).  The  double 


!§§  138,  1391  ACIDS  OF  THE  PROPIOLIC  SERIES.  173 

bond  is  situated  at  the  centre  of  the  chain,  the  constitution  of  oleic 
acid  being 

CH3.(CH2)7-CH:CH.(CH2)7-COOH. 

This  constitution  is  inferred  from  the  products  of  careful  oxida- 
tion, which  yields  pelargonic  acid,  CgHiy-COOH,  and  azelalc  acid, 
HOOC-(CH2)7.COOH. 

138.  Olei'c  acid  reacts  in  a  remarkable  manner  with  nitrous  acid, 
even  when  brought  into  contact  with  a  mere  trace  of  this  substance. 
The  best  method  is  to  pass  the  red  gaseous  mixture  of  nitrogen 
peroxide  and  nitric  oxide,  obtained  by  heating  arsenic  trioxide  with 
nitric  acid,  into  olei'c  acid,  or  to  add  nitric  acid  of  specific  gravity 
1-25.  The  olei'c  acid  soon  solidifies,  having  been  converted  into  an 
isomeride,  elaldic  acid.  The  reaction  is  called  the  "elaidic  trans- 
formation." Other  acids  of  this  series  are  similarly  transformed: 
thus,  erucic  acid,  ^22^-^2,  is  converted  by  a  trace  of  nitrous  acid 
into  brassidic  acid. 

Elai'dic  acid  has  the  same  structural  formula  as  oleic  acid,  the 
double  bond  occupying  a  similar  position  in  the  molecule  of  each, 
since  each  acid  readily  forms  a  bromine  addition-product  from 
which  elimination  of  2HBr  yields  stearolic  acid, 


Oleic  and  elajdic     Bromine  addition-       Stearolic  acid 
acids  product 

Olei'c  acid  and  elaidic  acid  yield  the  same  hydroxystearic  acid  by  the 
addition  of  one  molecule  of  water,  a  reaction  effected  by  the  action 
of  concentrated  sulphuric  acid.  Their  isomerism  is,  therefore,  like 
that  of  erucic  acid  and  brassidic  acid,  analogous  to  the  isomerism 
of  the  two  crotonic  acids  (136). 

II.  ACIDS  OF  THE  PROPIOLIC  SERIES,  CnH2n_402. 

139.  The  acids  of  the  propiolic  series  have  one  triple  bond,  or 
two  double  bonds,  in  the  molecule.  The  first-named  are  formed 
by  the  action  of  carbon  dioxide  upon  the  sodium  compounds  of  the 
acetylene  hydrocarbons  : 

CH=CNa  +C02  =  CH=C  •  COONa. 

Sodium  propiolate 


174  ORGANIC  CHEMISTRY.  [§  140 

The  a-carbon  atom  of  these  acids  has  a  triple  bond,  and  such  acids 
are  very  readily  decomposed  into  an  acetylene  hydrocarbon  and 
CO2;  f°r  example,  by  heating  their  silver  salts. 

A  general  method  for  the  preparation  of  acids  with  triple  bonds 
involves  the  addition  of  two  bromine  atoms  to  acids  containing  a 
double  bond,  and  subsequent  elimination  of  2HBr: 

CH3  •  CH  :  CH  •  COOH  -*  CH3  .  CHBr  -  CHBr  .  COOH  -> 

Crotonic  acid  Dibromobutyric  acid 

->CH8-C5C-COOH. 

Tetrolic  acid 

140.  In  presence  of  concentrated  sulphuric  acid,  substances 
with  a  triple  bond  take  up  water  with  formation  of  ketones  (125)  : 


In  this  manner  stearolic  acid  is  converted  into  a  ketostearic  acid  of 
the  formula 

C8H17.CO-CH2.(CH2)7.COOH, 

and  treatment  with  hydroxylamine  transforms  this  into  the  corre- 
sponding oxime: 

C8H17.C-CH2.(CH2)7.COOH. 
NOH 

Under  the  influence  of  concentrated  sulphuric  acid,  this  oxime 
undergoes  the  BECKMANN  transformation  (103),  among  the  pro- 
ducts being  the  substituted  acid  amide 


C8H17.CO 

(CH2)8.COOH, 


\^  '^S 

U 


which  is  proved  to  have  this  formula  by  its  decomposition  into 
pelargonic  acid,  CsH17-COOH,  and  the  9-aminononoi'c  *  acid, 
NH2-(CH2)s-COOH,  by  the  action  of  fuming  hydrochloric  acid. 
This  is  a  confirmation  of  the  constitution  above  indicated  for  olei'c 
acid  and  elaidic  acid,  since  they  can  be  converted  into  stearolic 
acid  in  the  manner  already  described. 

*  If  the  carboxyl-carbon  atom  is  denoted   by  1,  the  amino-group  is   in 
union  with  the  ninth  carbon  atom  of  the  chain. 


UNSATURATED  ALDEHYDES  AND  KETONES 


141.  The  lowest  unsaturated  aldehyde  is  acraldehyde  or  acrolein, 
CH2:CH-CHO.  It  is  obtained  by  removal  of  water  from  glycerol 
(153),  effected  by  heating  with  potassium  pyrosulphate,  K2S2C>7. 
It  is  a  colourless  liquid,  boiling  at  52-4°,  and  has  an  extremely 
powerful,  penetrating  odour,  to  which  it  owes  its  name  (acer, 
sharp,  and  oleum,  oil).  The  disagreeable,  pungent  smell  produced 
when  a  tallow  candle  or  an  oil-lamp  is  extinguished  is  due  to  the 
formation  of  acraldehyde.  On  reduction,  it  yields  allyl  alcohol, 
from  which  it  is  regenerated  by  careful  oxidation.  It  is  converted 
into  acrylic  acid  by  further  oxidation. 

It  has  the  properties  peculiar  to  aldehydes — the  susceptibility 
to  reduction  and  oxidation,  resinification  in  presence  of  alkalis, 
and  the  power  of  forming  polymerization-products.  It  possesses 
this  last  property  in  such  a  marked  degree  that  it  usually  becomes 
completely  converted  into  a  polymeride  in  the  course  of  a  few  days 
or  even  hours,  probably  under  the  catalytic  influence  of  traces  of 
impurities.  The  presence  of  the  double  bond  in  acraldehyde 
modifies  to  some  extent  the  aldehydic  character.  This  is  exhibited 
in  its  behaviour  towards  ammonia,  with  which  it  does  not  com- 
bine like  acetaldehyde  (104),  but  in  accordance  with  the  equation 

2C3H4O  +  NH3  =C6H9ON  +  H2O. 

Acraldehyde-ammonia  is  an  amorphous,  basic  substance,  is 
soluble  in  water,  and  in  its  appearance  and  behaviour  towards 
water  bears  a  close  resemblance  to  glue. 

Acraldehyde  does  not  unite  with  one  molecule  of  an  acid  sul- 
phite, but  with  two,  yielding  a  compound  from  which  the  aldehyde 
cannot  be  regenerated  by  the  action  of  acids,  which  eliminate  only 

175 


176  ORGANIC   CHEMISTRY.  [§§  142,  143 

one  molecule  of  the  acid  sulphite.     This  indicates  that  the  other 
molecule  of  acid  sulphite  has  been  added  at  the  double  bond. 

142.  Crotonaldehyde,  CH3.CH:CH^CHO,  results  on  elimination 

of  water  from  aldol,  CH3.CHfOH|.CHjH|  .a1?  (106),  by  heating  to 

\j 


140°.  It  is  a  liquid  boiling  at  104°-105°,  and  is  converted  by  oxida- 
tion with  silver  oxide  into  solid  crotonic  acid  (136),  proving  that  it 
has  the  constitution  indicated. 

TT 

Propiolaldehyde.  CH=C-C,<C~,  can  be    obtained  from  acroloin 

acetal  by  the  addition  of  two  bromine  atoms,  and  subsequent 
removal  by  means  of  caustic  potash  of  2HBr  from  the  addition- 
product  thus  formed: 


Acrolelnacetal  Dibromo-compound 

~>CH^C'C(O 

Propiolaldehydeacetal 

Propiolaldehydeacetal  is  converted  by  warming  with  dilute  sul- 
phuric acid  into  the  corresponding  aldehyde,  which  has  the  same 
irritating  action  on  the  mucous  membrane  as  acrolein. 

The  behaviour  of  propiolaldehyde  towards  alkalis  is   remark- 
able.    It  decomposes  into  acetylene  and  formic  acid: 


CH=C.CHO  +NaOH  =CH=C  - 

\0 

143.  An  important  unsaturated  aldehyde  is  geranial  (citral), 
CioHi6O,  characterized  by  its  agreeable  odour.  It  is  a  constituent 
of  various  essential  oils;  among  them  oil  of  orange-rind,  the  cheap 
oil  of  lemon-grass,  and  oil  of  citron.  At  the  ordinary  temperature 
it  is  liquid,  and  boils  at  110°-112°  under  a  pressure  of  12  mm.  Its 
aldehydic  nature  is  shown  by  its  reduction  to  an  alcohol,  gcraniol, 
and  its  oxidation  to  an  acid  with  the  same  number  of  carbon 
atoms,  geranic  acid. 

Geranial  has  the  structural  formula 


§  143]         UNSATURATED  ALDEHYDES  AND  KETONES.  177 

since  on  oxidation  it  yields  acetone,  lamilic  acid  (234),  and  carbon 
dioxide,  the  molecule  breaking  down  at  the  double  bonds: 


Geranial 


Acetone  Laevulic  acid  Carbon  dioxide 

When  boiled  with  a  solution  of  potassium  carbonate,  geranial 
takes  up  one  molecule  of  water,  .forming  methylheptenone  and  acetal- 
dehyde  : 

Cgs  >C=CH.CH2.CH2.C(CH3)=CH.C^-> 

Geranial 


Methylheptenone  Acetaldehyde 

On  oxidation,  methylheptenone  also  yields  acetone  and  laevulic 
acid.  This  reaction  indicates  its  constitution,  which  is  further 
proved  by  synthesis. 

Baryta-water  converts  a  mixture  of  geranial  and  acetone  into 
a  condensation-product,  pseudoionone; 

(CH3)2C=CH.CH2.CH2.C(CH3)=CH.CHO+H2CH.CO-CH3  = 

Geranial  Acetone 

=  H2O  +  (CH3)  2C=CH  •  CH2  •  CH2  •  C(CH3)  =CH  -  CH—  CH  •  CO  •  CH3. 

pseudolonone 

When  boiled  with  dilute  sulphuric  acid,  pse^oionone  yields 
ionone: 

CHs  CH.}  CH3  CH3 


c  c 

/  /\ 

HC       CH-CH:CH-CO-CH3-*H2C       CH-CH:CH.CO-CH3. 

II!  II 

C*CH3  H2C       C*CH3 

\/  \7 

CH2  CH 

pseudolonone  Ionone 


178  ORGANIC  CHEMISTRY.  §143] 

The  structure  of  ionone  is  proved  by  its  decomposition-products. 
It  is  manufactured  as  an  artificial  perfume,  as  it  has  a  powerful, 
violet-like  odour,  and  is  closely  related  to  irone,  the  active  principle 
of  violets.  The  formula  of  irone  is 


HC       CH.CH:CH.CO-CH3, 

II      i 

HC       CH.CH3 


CH2 


which  differs  from  that  of  ionone  only  in  the  position  occupied  by 
the  double  bond  in  the  carbon  ring. 


COMPOUNDS  CONTAINING  MORE  THAN  ONE 
SUBSTITUENT. 


I.  HALOGEN  DERIVATIVES  OF   METHANE. 

144.  The  halogen  derivatives  of  the  saturated  hydrocarbons 
obtained  by  replacement  of  a  single  hydrogen  atom  by  halogen  are 
called  alkyl  halides,  and  are  described  in  52-53.  This  chapter 
treats  of  the  compounds  formed  by  exchange  of  more  than  one 
hydrogen  atom  for  halogen. 

It  is  possible  to  replace  all  four  hydrogen  atoms  in  methane,  ia 
successive  stages,  by  the  direct  action  of  chlorine  or  bromine  in 
presence  of  sunlight.  Iodine  does  not  react  with  methane,  or  with 
its  homologues,  while  the  action  of  fluorine  is  very  energetic,  effect- 
ing complete  substitution. 

In  practice,  however,  this  is  not  the  method  adopted  for  the 
preparation  of  the  compounds  CH2X2,  CHX3,  or  CX4.  They  are 
obtained  from  the  trihalogen  derivatives:  these  are  readily  prepared 
by  another  method,  and  on  chlorination  or  bromination  yield  tetra- 
chloromethane  or  te  trabro  mo  methane ;  on  reduction  they  are  con- 
verted into  dihalogen-substituted  methanes.  On  account  of  their 
important  therapeutic  properties,  the  compounds  CHX3  are  pre- 
pared on  the  large  scale. 

Chloroform,  CHC13. 

145.  Chloroform  is  obtained  by  distilling  alcohol — or  on  the 
manufacturing  scale,  acetone — with  bleaching-powder.  This  reac- 
tion involves  simultaneous  oxidation  and  chlorination,  and  it  is 
assumed  that  aldehyde  is  first  produced  by  oxidation  of  the  alcohol, 
and  is  then  transformed  into  trichloroaldehyde,  or  chloral,  CC13-CHO. 

179 


180  ORGANIC  CHEMISTRY.  [§  145 

This  substance  is  converted  by  bases,  in  this  instance  by  the 
slaked  lime  present  in  the  bleaching-powder,  into  chloroform  and 
formic  acid  (201). 

Chloroform  is  a  liquid  boiling  at  61°,  and  solidifying  at  —70°. 
Its  specific  gravity  at  15°  is  1«498:  it  is  very  slightly  soluble  in 
water,  and  possesses  a  characteristic  ethereal  odour  and  sweet  taste. 
In  1847,  SIMPSON  discovered  that  its  prolonged  inhalation  pro- 
duces unconsciousness,  whence  it  derives  its  value  as  an  anaesthetic 
in  surgical  operations. 

Its  use  for  this  purpose  is  not  wholly  unattended  with  danger. 
Notwithstanding  the  fund  of  experience  resulting  from  the  fre- 
quency of  its  application,  it  occasionally  happens  that  the  inhala- 
tion of  chloroform  is  attended  by  fatal  results.  Ordinary  ether  and 
ethyl  chloride  are  less  dangerous,  do  not  produce  such  disagreeable 
after-effects,  and  hence  have  latterly  been  preferred  as  anaesthetics 
(56). 

Chloroform  is  a  somewhat  unstable  substance,  decomposing 
under  the.  influence  of  light  and  air,  and  yielding  chlorine,  hydro- 
chloric acid,  and  carbon  oxychloride,  COC12.  A  considerable 
amount  of  this  oxy-derivative  is  produced  by  bringing  chloroform- 
vapour  into  contact  with  a  flame.  Its  suffocating  effect  renders 
it  very  dangerous.  The  decomposition  of  the  liquid  can  be  almost 
prevented  by  adding  one  per  cent,  of  alcohol,  and  keeping  the 
chloroform  in  bottles  of  non-actinic  glass. 

The  halogen  atoms  of  chloroform  take  part  in  double  decom- 
positions :  thus,  sodium  ethoxide  yields  the  ethyl  ester  of  ortho- 
formic  acid: 


CH|C13  +3Na|  'OC2H5= CH(QC2H5)3  +3NaCL 

Formic  acid  can  be  obtained  by  warming  chloroform  with  dilute 
alkalis,  orthoformic  acid  being  probably  formed  first,  although  it 
has  not  been  isolated.  When  chloroform  is  treated  with  a  40  per 
cent,  aqueous  solution  of  caustic  potash,  carbon  monoxide  is  evolved: 
it  is  assumed  that  chloromethylene,  CC12,  is  formed  as  an  inter- 
mediate product. 

When  chloroform  is  warmed  with  alcoholic  ammonia  and 
caustic  potash,  its  three  chlorine  atoms  are  replaced  by  nitrogen, 
with  production  of  potassium  cyanide.  The  formation  of 


§  146]  IODOFORM.  181 

triles  from  chloroform,  alcoholic  potash,  and  primary  amines,  has 
been  already  mentioned  (77). 

Exposure  to  dark  electric  discharge  converts  chloroform  into 
a  series  of  highly  chlorinated  products,  such  as  C2C14,  C2HC15, 
C2C16;  C3HCl7,  and  others  of  similar  type. 

Methylene  chloride,  CH2C12,  is  obtained  from  chloroform  by  reduc- 
tion with  zinc  and  hydrochloric  acid  in  alcoholic  solution.  It  is  a 
liquid,  boils  at  40°,  and  has  a  specific  gravity  of  1  -337. 

Tetrachloromethane,  or  carbon  tetrachloride,  CC14,  produced  by 
the  action  of  chlorine  on  chloroform  or  carbon  disulphide,  is  also  a 
liquid,  and  boils  at  76°.  When  heated  with  excess  of  water  at  250° 
it  yields  HC1  and  CO2.  Its  specific  gravity  is  1-593  at  20°:  the 
high  specific  gravities  of  these  polychloro-compounds  is  noteworthy. 
The  bromine  and  iodine  compounds  are  specifically  much  heavier 
than  the  corresponding  chlorine  compounds. 

Bromoform,  CHBr3,  is  obtained  by  methods  analogous  to  the 
preparation  of  chloroform.  It  melts  at  7-8°,  boils  at  151°,  and  has 
a  specific  gravity  of  2«904  at  15°.  It  is  used  for  therapeutic  pur- 
poses. 

lodoform,  CHI3. 

146.  lodoform  is  a  substance  of  great  importance,  and  is  ob- 
tained from  alcohol  by  the  action  of  potassium  carbonate  and 
iodine.  The  intermediate  product  iodal,  CIs'CHO,  analogous  to 
chloral,  has  not  been  isolated.  On  the  manufacturing  scale  acetone, 
.being  less  expensive  than  alcohol,  is  often  employed. 

lodoform  can  also  be  prepared  by  the  electrolysis  of  a  solution 
containing  60  g.  of  potassium  iodide,  20  g.  of  sodium  carbonate,  and 
80  c.c.  of  alcohol  per  400  c.c.,  the  temperature  being  kept  between 
60°  and  65°.  Iodine  is  liberated  at  the  anode,  so  that  the  alcohol, 
potassium  carbonate,  and  iodine  necessary  to  the  formation  of 
iodoform  are  all  present  in  the  mixture.  By  this  method  about  80 
per  cent,  of  the  potassium  iodide  is  converted  into  iodoform,  the 
remainder  of  the  iodine  being  obtained  as  potassium  iodate.  The 
formation  of  iodate  can  be  avoided  to  a  great  extent  by  surrounding 
with  parchment  the  cathode,  at  which  caustic  potash  is  formed: 
this  prevents  contact  of  the  potassium  carbonate  with  the  iodine  set 
free  at  the  anode. 

lodoform  is  a  so)id,  and  crystallizes  in  yellow  hexagonal  plates, 
-well-developed  crystals  about  a  centimetre  in  length  being  obtained 
by  the  slow  evaporation  of  a  solution  in  anhydrous  acetone.  It 


182  ORGANIC  CHEMISTRY.  [§  147 

has  a  peculiar,  saffron-like  odour,  sublimes  very  readily,  and  melts 
at  119°. 

These  characteristic  properties  of  iodoform  make  its  formation  an 
important  test  for  alcohol,  although  aldehyde,  acetone,  and  several 
other  substances  similarly  yield  iodoform.  Substances  containing 
the  group  CH3-C  in  union  with  oxygen  answer  to  the  iodojorm- 
test.  It  is  carried  out  by  adding  iodine  to  the  liquid  under  examina- 
tion, and  then  caustic  potash  drop  by  drop  until  the  colour  of  the 
iodine  vanishes.  If  a  considerable  quantity  of  alcohol  is  present, 
a  yellow  precipitate  forms  at  once:  if  only  traces,  the  precipitate 
forms  after  a  time.  The  reaction  is  sufficiently  delicate  to  show 
traces  of  alcohol  in  a  sample  of  well-water  or  rain-water,  after  con- 
centration by  repeated  distillation,  the  first  fraction  in  each  case 
being  collected. 

Iodoform  is  employed  in  surgery  as  an  antiseptic.  It  is  note- 
worthy that  it  does  not  kill  the  bacteria  directly,  its  action  on  the 
micro-organisms  being  subsequent  to  a  decomposition  resulting, 
under  the  influence  of  the  heat  of  the  body,  from  fermentation 
induced  by  the  matter  exuded  from  the  wound. 

Methylene  iodide,  CH2l2,  is  a  liquid,  and  is  obtained  by  the 
reduction  of  iodoform  with  hydriodic  acid;  phosphorus  is  added  to 
regenerate  the  hydriodic  acid.  Its  specific  gravity,  3*292  at  18°, 
is  remarkably  high. 


H.  HALOGEN  DERIVATIVES  OF    THE    HOMOLOGUES    OF  METHANE. 

147.  It  is  evident  that  among  these  derivatives  numerous  cases 
of  isomerism  are  possible.  For  example,  replacement  by  chlorine 
of  three  hydrogen  atoms  in  normal  pentane  may  yield  several  dif- 
ferent compounds:  thus,  a  methyl-group  may  be  converted  into 
CCls;  two  chlorine  atoms  may  replace  the  hydrogen  of  one  methyl- 
ene-group,  while  the  third  replaces  another  hydrogen  atom  in  the 
molecule;  or  the  three  chlorine  atoms  may  unite  with  different 
carbon  atoms;  and  so  on. 

The  preparation  of  many  of  the  halogen  compounds  included 
under  this  heading  has  already  been  described,  the  compounds 
CnH2n+i'CHX2  and  CpH2p+1-CX2-CqH2q+1  being  obtained  by  the 


§  148]  HALOGEN  DERIVATIVES  OF  PARAFFINS.  183 

action  of  phosphorus  pentahalide  on  aldehydes  and  ketones  respect- 
ively (98)  .  Compounds  with  two  halogen  atoms  attached  to  two 
adjoining  carbon  atoms  are  obtained  by  addition  of  halogen  to  the 
hydrocarbons  CnH2n;  those  having  four  halogen  atoms,  two  being 
directly  united  to  each  of  two  adjoining  carbon  atoms,  are  produced 
by  addition  of  halogen  to  hydrocarbons  with  a  triple  bond;  while 
compounds  of  the  type 


CptL2p_j_i  *  CH.%.  •  CH  A.  •  CfH2r  *  CHX  •  CHX  •  Cmli2m+i 

result  on  addition  of  halogen  to  the  hydrocarbons  CnH2n_4,  con- 
taining two  double  bonds;  etc. 

A  method  for  the  preparation  of  compounds  rich  in  halogen 
from  the  saturated  hydrocarbons  is  the  exchange  of  one  hydrogen 
atom  for  halogen,  elimination  of  hydrogen  halide  by  means  of  alco- 
holic potash,  halogenation  of  the  hydrocarbon  CnH2n  thus  obtained, 
removal  of  HX,  renewed  halogenation  of  the  product,  and  so  on. 

CH3-CH3->CH3-CH2Cl-HCl->CH2:CH2+2Cl-> 

Ethane  Ethyl  chloride  Ethylene 


-»  CH2C1  •  CH2C1  -  2HC1 

Ethylene  chloride  Acetylene 

-+CHC12  •  CHC12-  HC1  -*  CHC1  :  CC12  +2C1  -» 

Tetrachloroethane  Trichloroethylene 

->  CHC12  •  CC13  -  HC1  -»  CC12  :  CC12  +  2C1  ->  CC13  -  OC13. 

Pentachloroethane  Tetrachloroethylene  Hexachloroethane 

A  method  for  the  preparation  of  polybromo-compounds  was 
discovered  by  VICTOR  MEYER,  and  involves  the  direct  action  of 
bromine  on  the  hydrocarbons  of  the  series  CnH2n+2  in  presence  of  a 
small  quantity  of  anhydrous  iron  bromide,  or  iron-wire.  These 
conditions  greatly  facilitate  substitution,  each  carbon  atom  of  a 
normal  chain  taking  up  only  one  bromine  atom.  Thus,  propane 
yields  tribromohi/drin,  CH2Br-CHBr»CH2Br,  since  the  product  is 
identical  with  the  addition-product  obtained  by  the  action  of  bro- 
mine on  allyl  bromide,  CH2:CH-CH2Br  (130). 

Nomenclature  and  Individual  Members. 

148.  The  notation  adopted  by  the  Chemical  Society  of  London 
is  that  "  In  open-chain  compounds  Greek  letters  must  be  used  to 


184  .       ORGANIC  CHEMISTRY.  [§  148 

indicate  the  position  of  a  substituent,  the  letter  a  being  assigned 
to  the  first  carbon  atom  in  the  formula,  except  in  the  case  of  CN", 
CHO,  and  C02H."  Thus,  CH3-CH2.CH2.CH2I  is  a-iodobutane; 
CH3.CH2-CH2.CN  a-cyanopropane;  CH2Br.CH2.CH2Br  aaf- 
dibromopropane;  CH2Br'CHBr»CH3  a/?-dibromopropane. 

Only  a  few  of  the  numerous  compounds  of  this  group  will  be 
described. 

Tetrachloroethane,  CHC1;>»CHC12,  is  prepared  technically  by  the 
interaction  of  chlorine  and  acetylene,  with  antimony  pentachloride 
as  catalyst.  It  is  a  liquid  boiling  at  147°.  When  it  is  boiled  with 
milk  of  lime,  hydrochloric  acid  is  eliminated,  with  formation  of 
trichloroethylene,  CC12:CHC1,  a  liquid  boiling  at  88°.  On  addition 
of  zinc-dust  to  an  aqueous  suspension  of  tetrachloroethane,  heat  is 
developed,  and  pure  dichloroethylene,  CHC1:  CHC1,  distils.  It  is  a 
liquid  boiling  at  55°.  All  these  substances  are  excellent  solvents 
for  fats  and  oils;  they  also  dissolve  sulphur  readily,  and  are 
employed  in  vulcanizing  caoutchouc. 

Ethylene chloride,  CH2C1-CH2C1,  is  called  "Dutch  Liquid,"  or  the 
"Oil  of  the  Dutch  Chemists,"  it  having  been  first  prepared  at  the 
end  of  the  eighteenth  century  by  four  Dutch  chemists,  DEIMAN, 
BONDT,  PAETS  VAN  TROOSTWYK,  and  LAUWERENBURGH,  by  the 
action  of  chlorine  upon  ethylene.  It  is  a  liquid  boiling  at  84-9°, 
and  has  a  specific  gravity  of  1-28  at  0°. 

Hexachloroethane  (perchloroethane) ,  C2C16,  is  formed  by  the  direct 
union  of  carbon  and  chlorine  under  the  influence  of  a  powerful  arc- 
discharge  between  carbon  poles  in  an  atmosphere  of  chlorine. 

Ethylene  bromide  is  employed  for  syntheses  and  as  a  solvent. 
It  is  prepared  by  passing  ethylene  into  bromine  covered  with  a 
layer  of  water  to  prevent  evaporation,  the  addition  taking  place 
very  readily.  Ethylene  bromide  is  a  colourless  liquid  of  agreeable 
odour,  solidifies  at  8°,  boils  at  131°,  and  has  a  specific  gravity  of 
2- 189  at  15°. 

Trimethylene  bromide,  CH2Br»CH2»CH2Br,  aa'-dibromopropane, 
also  plays  an  important  part  in  syntheses,  and  is  obtained  by  addi- 
tion of  HBr  to  allyl  bromide,  CH2:  CH»CH2Br,  produced  from  allyl 
alcohol.  This  method  of  formation  suggests  the  constitution 
CH3'CHBr»CH2Br,  that  of  the  addition-product  obtained  by  the 
action  of  bromine  upon  propylene,  CH3»CH:CH2.  Since  the  two 
compounds  are  not  identical,  trimethylene  bromide  must  have  the 


§§  149,  150] 


POLYHYDRIC  ALCOHOLS. 


185 


aa'-formula.     It  is  a  liquid,  boiling  at  165°,  and  has  a  specific  gravity 
of  1-974  at  17°. 

Pcntamethylene  dibromide  is  mentioned  in  388. 

III.   POLYHYDRIC   ALCOHOLS. 

149.  When  more  than  one  hydrogen  atom  of  a  saturated  hydro- 
carbon is  replaced  by  hydroxyl,  it  is  theoretically  possible  to  have 
more  than  one  hydroxyl-group  in  union  with  a  single  carbon  atom, 
or  to  have  each  attached  to  a  different  one.     It  should  be  possible 
to  obtain  compounds  of  the  first  class  by  replacement  of  halogen 
by   hydroxyl  in  the   halogen  derivatives  R-CHX2,  R-CX3,  and 
R'CX2-R'.     Silver  acetate  converts  halogen  compounds  of  this 

type  into  stable  acetates,  such  as  G/H2<Qpp  !Q-     On  saponifica- 

tion,  however,  dihydric  alcohols  like  CH2(OH)2  are  not  obtained, 
but  aldehydes  result  by  elimination  of  one  molecule  of  water.  When 
compounds  of  the  type  RCC13  are  treated  with  sodium  ethoxide, 
substances  with  the  general  formula  R '0(002115)3,  called  ortho- 
esters,  are  obtained.  On  saponification  R-C(OH)3  does  not  result, 
the  corresponding  acid  being  formed  instead,  through  loss  of  water. 

Ethers  of  dihydric  alcohols,  such  as  CH3  •  CH  <  ~ n2Tj5,  are  known, 

UL2-ti5 

and  are  called  acetals  (104,  2).  The  saponification  of  these  sub- 
stances does  not  yield  R'CH(OH)2,  but  an  aldehyde.  It  follows 
from  these  facts  that  compounds  with  more  than  one  hydroxyl-group 
attached  to  the  same  carbon  atom  are  unstable,  although  it  is  some- 
times possible  to  obtain  such  compounds  (201,  230,  and  234). 

Many  compounds  are  knowTi  containing  several  hydroxyl- 
group:^  of  which  not  more  than  one  is  in  union  with  each  carbon 
atom. 

i.  Glycols  or  Dihydric  Alcohols. 

150.  The  ylycols  are  obtained  from  the  corresponding  halogen 
compounds  analogously  to  the  monohydric  alcohols  (39) : 


•O-OC-CHs     CH2 
— >  CH2 


0-OC-CH3    CH2 


Trimethylene 
bron  ide 


Trimethyleneglycol 
diacetate 


OH    CH2.OH 


OH     CH2-OH 

Trimethylene- 
glycol 


186  ORGANIC  CHEMISTRY.  [§  150 

The  exchange  of  halogen  for  hydroxyl  can  be  brought  about  by 
treatment  with  acetate  of  silver  or  the  acetate  of  an  alkali-metal, 
and  saponification  of  the  diacetate  thus  obtained.  It  can  also  be 
effected  directly  by  boiling  with  sodium-carbonate  solution,  or  water 
and  lead  oxide. 

Glycols  of  the  type  R-CHOH-CHOH-R,  with  the  CHOH- 
groups  in  direct  union,  are  formed  from  defines  either  through  the 
medium  of  their  bromine  addition-products,  or  by  the  direct  addi- 
tion of  two  OH-groups  by  means  of  careful  oxidation  with  potassium 
permanganate.  Thus,  ethylene  yields  the  simplest  dihydric  alcohol, 
called  glycol: 


Another  method  for  the  formation  of  glycols  of  this  type  consists 
in  the  reduction  of  ketones.  This  may  be  either  carried  out  with 
sodium  in  aqueous  solution,  or  by  electrolysis.  Acetone  yields  pma- 
cone  and  isopropyl  alcohol.  Glycols  of  the  type  of  pinacone  —  called 
pinacones  —  can  be  obtained  without  admixture  of  a  secondary  alco- 
hol by  reduction  of  aldehydes  or  ketones  with  magnesium-amalgam, 
addition-products  being  first  formed  with  evolution  of  heat: 

2CH3.C^+Mg=CH3.CH  -  CH-CH, 


or 


Water   decomposes  the  addition-product,   with  formation   of  the 
-unacone  : 


CIV*  9 9<CHl+2H8O=p23>C(OH)— C^(OH)+MgO. 


O-Mg.O 
The  constitution  of  pinacone  is  indicated  by  its  synthesis: 

CH3.CO.CH3    H        CHa.C(OH).CH3 
CH3.CO.CH3    H        CH3.C(OH).CH* 

Acetone  Pinacone 


§  150]  GLYCOLS.  187 

When  distilled  with  dilute  sulphuric  acid,  pinacone  undergoes  a 
remarkable  intramolecular  transformation,  explicable  on  the  assump- 
tion that  a  hydroxyl-group  changes  place  with  a  methyl-group : 

/OH  X0|H 

<CH3)2C(OH)  .C(-CH3  -» (CH3)3C .C^(OH:  -  H2O  =  (CH,)aC  -  CO  *CH3. 

Pinacone  \CH3  C  H  Pinacolin 

The  constitution  of  pinacolin  may  be  deduced  from  its  synthesis  by 
the  action  of  zinc  methide  on  trimethylacetyl  chloride,  (CH3)3C-COCI, 
and  ip  other  ways. 

Most  of  the  glycols  are  colourless,  viscous  liquids  of  sweet  taste, 
whence  the  series  derives  its  name.  Their  boiling-points  and  speci- 
fic gravities  are  considerably  higher  than  those  of  the  monohydric 
alcohols  with  the  same  number  of  carbon  atoms.  Thus,  glycol  boils 
at  197-5°,  and  ethyl  alcohol  at  78°:  at  0°  the  specific  gravity  of 
glycol  is  1-128,  and  of  ethyl  alcohol  0-806.  The  nature  of  the 
hydroxyl-groups  in  glycol  and  that  in  the  monohydric  alcohols  is 
perfectly  analogous:  exchange  of  OH  for  halogen,  the  formation  of 
ethers,  esters,  and  alkoxides,  and  the  oxidation  of  primary  glycols 
to  aldehydes  and  acids,  may  take  place  in  connection  with  one  or 
both  of  the  hydroxyl-groups.  For  instance,  the  compounds 
CH2OH.CH2C1,  glycolchlorohydrin;  CH2OC2H5.CH2OH,  glycol- 
monoethyl  ether;  CH2OC2H5.CH2OC2H5,  glycol  diethyl  ether;  etc.; 
are  known.  The  glycols  possess,  however,  one  property  due  to  the 
presence  of  two  hydroxyl-groups,  the  power  of  forming  anhydrides. 
The  first  member  of  the  series,  glycol,  CH2OH-CH2OH,  does  not 
yield  an  anhydride  by  the  direct  elimination  of  water,  but  a  com- 
pound of  the  formula  C2H4O  is  obtained  by  first  replacing  one 
liydroxyl-group  by  Cl  and  then  eliminating  HC1: 

CH, 


\^£121^1  \^X12\ 

|           -HC1  =   |       >0. 

CH2OH  CH/ 

Glycolchlorohydrin  Ethylene  oxide 


This  compound,  ethylene  oxide,  boils  at  14°,  and  is  therefore  gas- 
eous at  ordinary  temperatures:  it  readily  takes  up  water,  forming 
glycol;  or  hydrochloric  acid,  forming  glycolchlorohydrin.  To 
ethylene  oxide  is  assigned  the  constitutional  formula  indicated, 
because  it  yields  ethylene  chloride  when  treated  with  phosphorus 
pentachloride,  the  oxygen  atom  being  replaced  by  two  chlorine 


138  ORGANIC  CHEMISTRY.  [§151 

CH2 

atoms.     If  the  compound  had  the  constitution    ||  ,  which  is 

CHOH 

also  possible  but  less  probable  (131),  it  would  not  yield  ethylene 
chloride  when  thus  treated. 

Some  of  the  higher  homologues  of  glycol  with  a  chain  of  four 
or  five  carbon  atoms  between  the  hydroxyl-groups  yield  anhydrides 
with  a  constitution  analogous  to  that  of  ethylene  oxide.  They 
show  a  marked  diminution  in  the  power  of  forming  addition- 
products  with  water;  or,  in  other  words,  the  closed  chain  of  carbon 
atoms  and  one  oxygen  atom  is  more  stable  than  in  ethylene  oxide 
itself. 


2.  Trihydric  Alcohols. 

151.  The  principal  representative  of  the  group  of  trihydric 
alcohols  is  glycerol,  or  "glycerine,"  C3H5(OH)3.  In  accordance 
with  the  rule  that  two  hydroxyl-groups  cannot  attach  themselves 
to  the  same  carbon  atom,  glycerol  can  only  have  the  structure 

CH2OH.CEOH-CH2OH. 

This  structure  finds  support  in  other  proofs. 

1  .  On  careful  oxidation  of  allyl  alcohol  by  means  of  potassium 
permanganate,  two  OH-groups  are  added  at  the  position  of  the 
double  bond  : 

CH2  :  CH  .  CH2OH  -»  CH2OH  -  CHOH  -  CH2OH. 


2.  When  glycerol,  CsHgOs,  is  carefully  oxidized,  glyceric  acid, 
is  first  formed,  corresponding  to  the  formation  of  acetic 
acid,  C2H402>  from  ethyl  alcohol,  C2H6O,  by  exchange  of  two 
hydrogen  atoms  for  one  oxygen  atom:  this  indicates  that  glycerol 
contains  one  —  CH2OH-group.  Further  oxidation  converts  gly- 
ceric acid  into  tartronic  acid,  CsH4O5,  two  hydrogen  atoms  being 
replaced  by  one  oxygen  atom,  with  formation  of  a  new  carboxyl- 
group.  Hence,  glycerol  contains  two  —  CH2OH-groups  in  the 
molecule,  so  that  its  '  constitution  is  CH2OH»CH2O'CH2OH. 
Since  tartronic  acid,  COOH-CH2O-COOH,  still  possesses  alcoholic 
properties,  the  group  CH2O  must  have  the  constitution  >CHOH,. 


§§  152,  153]  GLYCEROL. 

and  since  it  must  have  the  same  constitution  in  the  molecule 
of  glycerol,  the  structure  of  the  latter  is  proved  to  be 
CH2OH.CHOH.CH2OH. 

3.  A  further  proof  of  the  constitution  given  above  is  the  forma- 
tion of  glycerol  from  tribromohydrin  (147) . 

152.  Glycerol  is  a  colourless,  oily  liquid  of  sweet  taste,  is  very 
hygroscopic,  and  miscible  in  all  proportions  with  water  and 
alcohol,  but  insoluble  in  ether.  When  cooled  to  a  low  tempera- 
ture for  some  time,  it  solidifies,  but  the  crystals  thus  formed  do 
not  melt  below  17°.  It  boils  at  290°,  and  has  a  specific  gravity  of 
1-265  at  15°.  Its  chemical  behaviour  accords  completely  with 
the  constitution  of  a  trihydric  alcohol.  Thus,  it  yields  three 
esters,  by  replacement  of  one,  two,  or  three  hydroxyl-groups. 
When  borax  is  dissolved  in  glycerol  or  in  a  solution  of  this  sub- 
stance and  the  mixture  introduced  into  the  flame,  the  green  colour 
characteristic  of  free  boric  acid  is  observed:  on  this  reaction  is 
based  SENIER'S  test  for  glycerol. 

Since  glycerol  is  a  substance  which  plays  a  very  important  part  in 
the  economy  of  nature  as  a  constituent  of  the  fats  (154),  its  synthesis 
from  its  elements  is  of  great  interest.  This  was  effected  by  FRIEDEL 
and  SILVA,  the  starting-point  being  acetic  acid.  This  substance  can 
be  synthesized  from  its  elements  in  several  ways,  for  example  by 
the  oxidation  of  acetaldehyde  obtained  by  the  action  of  water  on 
acetylene  (125).  The  dry  distillation  of  calcium  acetate  gave  ace- 
tone, which  was  reduced  to  fsopropyl  alcohol.  On  elimination  of 
water  from  this  alcohol,  propylene  was  formed,  and  on  addition  of 
chlorine,  was  converted  into  propylene  chloride,  from  which  tri- 
chlorohydrin  was  obtained  by  treatment  with  iodine  chloride.  Tri  - 
chlorohydrin  was  converted  into  glycerol  by  heating  with  water  at 
170°: 


CH3.COOH  ->CH3.CO.CH3  ->CH3.CHOH.CH3  -^CH,.CH  :CH2  -^ 

Acetic  acid  Acetone  tsoPropyl  alcohol  Propylene 

-»CH3.CHC1.CH2C1  ->CH2C1.CHC1.CH2C1  ->CH2OH.CHOH.CH2OH. 

Propylene  chloride  Trichlorohydrin  Glycerol 

153.  Several  compounds,  difficult  to  prepare  otherwise,  can  be 
obtained  from  glycerol.  Among  them  are  allyl  alcohol,  allyl 
iodide,  acraldehyde,  and  isopropyl  iodide. 

Allyl  alcohol,  CH2:CH'CH2OH,  can  be  prepared  from  glycerol 


190 


ORGANIC  CHEMISTRY. 


[§153 


by  heating  it  with  oxalic  acid,  COOH-COOH.     Glyceryl  mono- 
formate  or  monojormin, 


CH2OH  -  CHOH  •  CH2  •  OCO 
H 


or 


CH2OH.CH.CH2OH 
» 


is  first  produced,  as  under  these  conditions  oxalic  acid  loses  one 
molecule  of  carbon  dioxide,  yielding  formic  acid,  [CQOJH — COOH, 
which  combines  with  the  glycerol  to  produce  monoformin.  When 
heated  more  strongly,  this  decomposes  into  ally  1  alcohol,  water, 
and  carbon  dioxide : 


CH2OH-CH 


OH]CH2|O-CO 


H 


CH2QH-CH— CH2[QH 


or 


Allyl  iodide  is  obtained  by  the  action  of  phosphorus  and  iodine 
on  anhydrous  glycerol : 


CH2fOH 


CH 
CH: 


OH+P 
OH 


CH2I 

I3  =  CHI+P03H3; 
CHoI 


CH 
CH 
CH2I 


f 

|I  -21  = 


CH2 

II    ' 
CH    , 

CH2I 


The  trl-iodohydrin,  C3H5I3,  probably  formed  as  an  intermediate 
product  in  this  reaction  is  unstable,  and  at  once  loses  two  atoms 
of  iodine,  yielding  allyl  iodide. 

Acraldehyde  (141)  results  by  elimination  of  water  from  glycerol: 

[OHH| 

CH2-C—  CHOH. 


CH2:C:CHOH  should  be  obtained,  but  immediately  changes  to 
acraldehyderCH2:CH.C^  (131). 

Large  quantities  of  acraldehyde  can  be  prepared  by  passing 
glycerol-vapour  over  anhydrous  magnesium  sulphate  at  3300-3400, 
the  yield  corresponding  with  60  per  cent,  of  the  glycerol  employed. 
For  the  preparation  of  small  quantities,  250  g.  of  glycerol  can  be 
heated  with  10  g.  of  potassium  pyrosulphate,  K2S207. 


§  154]  GLYCEROL.  191 

isoPropyl  iodide  is  formed  by  the  addition  of  water  to  a  mix- 
ture of  glycerol  with  iodine  and  phosphorus.  In  this  reaction 
propylene,  CH3«CH:CH2,  is  an  intermediate  product,  and  is 
evolved  in  the  free  state  if  insufficient  hydriodic  acid  is  present. 
By  the  addition  of  HI,  produced  by  the  interaction  of  iodine, 
phosphorus,  and  water,  zsopropyl  iodide  is  formed  from  the  pro- 
pylene  thus  generated: 

CH3.CH:CH2  +  HI  -  CH3-CHI.CH3. 

Propylene  rsoPropyl  iodide 

Formic  acid  (81)  is  usually  prepared  by  the  action  of  glycerol 
on  oxalic  acid.  As  previously  mentioned,  when  these  substances 
are  heated  together,  carbon  dioxide  is  evolved,  and  glyceryl 
monoformate  produced.  Formic  acid  is  obtained  from  the  latter 
by  saponification,  the  glycerol  being  simultaneously  regenerated 
by  the  addition  of  a  fresh  quantity  of  oxalic  acid,  C2H2O4,2H2O, 
the  water  of  crystallization  saponifying  the  ester,  and  the 
formic  acid  distilling  over.  The  glycerol  thus  regenerated 
is  again  converted  into  monoformin  by  the  freshly-added  oxalic 
acid,  and  the  ester  once  more  decomposed  by  the  addition  of  a 
further  quantity  of  oxalic  acid,  and  so  on.  It  is  thus  possible 
to  convert  unlimited  quantities  of  oxalic  acid  into  formic  acid  by 
means  of  a  given  quantity  of  glycerol. 

154.  Glycerol  occurs  in  nature  in  large  quantities  in  the  form 
of  esters.  The  fats  and  oils  are  glyceryl  tri-esters  of  the  higher 
fatty  acids  and  of  olei'c  acid:  glycerol  and  the  fatty  acids  are 
obtained  from  them  by  saponification  (85  and  95).  Glycerol 
is  also  present  in  small  proportion  in  the  blood. 

Saponification  of  the  esters  of  polyhydric  alcohols. — The  saponi- 
fication of  the  tri-esters  of  glycerol  with  caustic  soda  or  lime  takes 
place  in  stages,  the  di-esters  and  mono-esters  being  formed  as 
intermediate  products,  as  can  be  readily  proved.  On  complete 
saponification,  pure  tristearin,  or  glyceryl  tristearate  yields  only 
stearic  acid  and  glycerol,  so  that  if  no  intermediate  products  are 
formed,  a  partially-saponified  portion,  in  which  the  soap  produced 
has  been  decomposed  by  hydrochloric  acid,  and  the  glycerol  removed 
by  washing  with  water,  should  contain  only  unchanged  tristearin 
and  stearic  acid.  Neither  tristearin  nor  stearic  acid  can  yield  acetyl- 
derivatives  with  acetic  anhydride.  If  the  saponification  takes  place 


192  ORGANIC  CHEMISTRY.}  [§  155 

in  stages,  monostearin  and  distearin  should  be  formed,  and  the  free 
hydroxyl-groups  of  the  glyceryl-residue  in  these  compounds  should 
react  with  acetic  anhydride  to  form  acetyl-compounds.  On  treat- 
ment with  this  anhydride,  and  subsequent"  complete  saponification, 
acetic  acid  should  be  among  the  products,  and  it  has  been  proved 
by  experiment  that  this  is  so. 

When  glycol  diacetate  and  glyceryl  diacetate  are  saponified 
with  very  dilute  hydrochloric  acid,  the  velocity  of  saponification 
for  each  compound  differs  at  the  various  stages.  It  has  been  stated 
that  the  ratio  of  the  velocity-constant  of  glycol  diacetate  to  that 
of  the  monoacetate  is  as  2:1,  the  corresponding  ratio  for  the  glyceryl 
tri-esters,  di-esters,  and  mono-esters  being  as  3:2:1.  It  is  obvious 
that  during  saponification  a  molecule  containing  n  acid-radicals 
will  encounter  the  hydroxyl-ions  or  hydrogen  ions  n  times  as  often 
as  if  only  one  were  present.  It  follows  that  in  the  saponification 
of  poly-esters,  the  ratio  of  the  velocity-constants  of  the  individual 
stages  must  correspond  with  that  of  the  acid-radicals  present  in 
each  stage. 

Inversely,  the  fats  can  be  synthesized  from  glycerol  and  the 
fatty  acids:  for  instance,  tristearin  is  obtained  by  heating  glycerol 
with  excess  of  stearic  acid  under  reduced  pressure  at  200°  until 
separation  of  water  ceases. 

Many  fats  gradually  become  rancid,  and  develop  a  disagreeable 
smell  and  taste.  This  is  due  to  atmospheric  oxidation,  which  is 
facilitated  by  the  influence  of  light.  The  unsaturated  fatty  acids 
become  converted  into  others  containing  a  smaller  number  of  car- 
bon atoms,  and  with  a  characteristic  odour  and  taste. 

The  digestion  of  fats  is  attended  by  decomposition  into 
glycerol  and  fatty  acid,  effected  by  an  enzyme  present  in  the 
pancreas. 

155.  Glycerol  is  extensively  employed  in  the  arts  and  in  medi- 
cine. One  of  its  most  important  applications  is  to  the  preparation 
of  the  so-called  "  nitroglycerine."  This  explosive  has  a  mislead- 
ing name,  since  it  is  glyceryl  trinitrate, 

CH2O-N02 
CHO-NO2, 
CH2O-N02 

and  not  a  nitro-compound  (68) ;  for  on  saponification  with  alkalis 
it  yields  glycerol,  and  the  nitrate  of  the  corresponding  alkali -metal.. 


§  156]        TETRAHYDRIC  AND  POLYHYDRIC  ALCOHOLS.  193 

Nitroglycerine  is  prepared  by  bringing  glycerol  into  contact 
with  a  mixture  of  concentrated  sulphuric  acid  and  nitric  acid,  rise 
of  temperature  being  prevented.  Other  polyhydric  alcohols 
are  converted  analogously  into  nitrates.  After  a  time,  the  reac- 
tion-mixture is  poured  into  water,  whereupon  the  nitrate  separates 
in  the  form  of  an  oily,  very  explosive  liquid  of  faint,  headache- 
producing  odour.  It  can  be  purified  by  washing  with  water; 
when  perfectly  pure  it  does  not  explode  spontaneously. 

The  specific  gravity  of  nitroglycerine  is  1-6.  Its  metastable 
form  solidifies  at  2-2°,  and  its  stable  modification  at  12-2°. 

Nitroglycerine  is  a  liquid,  and  as  its  use  in  this  form  for  technical 
purposes  would  be  attended  with  difficulties,  it  is  mixed  with  infu- 
sorial earth  ("  kieselguhr"),  which  absorbs  it,  forming  a  soft,  plastic 
mass,  dynamite,  containing  usually  75  per  cent,  of  nitroglycerine  and 
25  per  cent,  of  the  earth.  Nitroglycerine  can  also  be  obtained  in 
the  solid  form  by  dissolving  in  it  a  small  amount  of  guncotton  (228), 
which  converts  it  into  an  elastic  solid  resembling  jujubes  in  con- 
sistence, called  "blasting  gelatine."  This  substance  has  the  advan- 
tage over  dynamite  of  not  leaving  any  solid  residue  after  explosion. 
Dynamite  cannot  be  used  as  ammunition,  its  velocity  of  explosion 
being  so  great  as  to  produce  an  impulse  too  violent  for  a  gun  to 
resist  without  bursting:  that  is,  it  exerts  a  "brisant"  or  detonating 
effect. 

3.  Tetrahydric  and  Polyhydric  Alcohols. 
156.  Among  the  tetrahydric  alcohols  is  erythritol, 
CH2OH  •  CHOH  •  CHOH .  CH2OH, 

which  is  a  natural  product.  It  contains  a  normal  carbon  chain, 
since  reduction  with  hydriodic  acid  converts  it  into  n-secondary 
butyl  iodide,  CH3.CHI-CH2.CH3. 

Examples  of  pentahydric  alcohols  are  arabitol  and  xylitol, 
C5H12Os,  which  are  stereo isomerides,  as  are  also  the  hexahydric 
alcohols  dulcitol  and  mannitol,  CeH^Oe,  both  of  which  are  found  in 
nature.  These  all  have  normal  carbon  chains,  since,  like  erythritol, 
they  yield  n-secondary  iodides  on  reduction  with  hydriodic  acid: 
thus,  mannitol  is  converted  into 

CH3  •  CH2 .  CHI  •  CH2  •  CH2  •  CH3. 


194  [ORGANIC  CHEMISTRY.  [§§  157, 158 

They  can  be  obtained  artificially  by  the  reduction  of  the  corre- 
sponding aldehydes  or  ketones,  dulcitol  being  formed  from, 
galactose,  and  mannitol  from  mannose  and  laBvulose.  The 
reason  for  assuming  their  stereoisomerism  is  explained  in  205, 
but  here  it  may  be  pointed  out  that  the  polyhydric  alcohols 
contain  asymmetric  carbon  atoms,  indicated  in  the  formulae  by 
asterisks: 

CH2OH.CHOH.CHOH.CHOH.CH2OH; 

Arabitol  and  Xylitol 

CH2OH  -  CHOH .  CHOH  •  CHOH .  CHOH .  CH2OH. 

Dulcitol  and  Mannitol 

157.  The  presence  of  polyhydric  alcohols  prevents  the  pre- 
cipitation of  the  hydroxides  of  copper,  iron,  and  other  metals  by 
means  of  alkalis.  Thus,  a  solution  of  copper  sulphate  and  glycerol 
does  not  yield  a  precipitate  of  copper  hydroxide  with  caustic 
potash.  This  is  due  to  the  formation  of  soluble  metallic  compounds 
of  the  polyhydric  alcohols,  the  hydroxyl-hydrogen  being  replaced 
by  the  metal.  The  acidic  nature  of  the  hydroxyl-group,  almost 
lacking  in  the  monohydric  alcohols,  is  therefore  in  some  measure 
developed  by  increase  in  the  number  of  these  groups  present  in  the 
molecule.  This  property  is  possessed  not  only  by  the  polyhydric 
alcohols,  but  also  by  many  other  compounds  containing  several 
hydroxyl-groups  (191). 


IV.  DERIVATIVES    CONTAINING    HALOGEN    ATOMS,    HYDROXYL- 
GROUPS,  NITRO-GROUPS,  OR  AMINO-GROUPS. 

158.  Only  a  few  of  the  numerous  compounds  belonging  to  this 
class  will  be  considered :  the  chemical  properties  of  its  members  are 
determined  by  the  substituents. 

No  compounds  containing  halogen  and  hydroxyl  in  union  with 
the  same  carbon  atom  are  known:  when  their  formation  might  be 
expected,  hydrogen  halide  is  eliminated,  with  production  of  alde- 
hydes or  ketones.  It  has  been  mentioned  more  than  once  that 
stable  alkyl-derivatives  of  compounds  themselves  unstable  or  un- 
known, such  as  the  ortho-esters,  exist  (149).  This  is  true  in  this 

Cl 
instance,  for  while  compounds  of  the  type  R-CH  <        are  unknown, 


§  158]  CHLOROETHERS  AND  CHLOROHYDRINS.  195 

Cl 

derivatives  of  the  formula  R'CH<,^  ^  ^         are  known.     rihese 

O-Lnli2n+l 

substances  are  called  chloroethers.  When  chlorine  is  passed  into 
ethyl  ether,  kept  cool  and  in  the  dark  to  avoid  explosion,  the 
hydrogen  atoms  are  replaced  by  chlorine.  The  monosubstitution- 
product  has  the  constitution 

CH3.CH2.0-CHC1-CH3, 

Monochloroether 

as  is  proved  by  the  action  of  sulphuric  acid,  under  the  influence  of 
which  it  takes  up  one  molecule  of  water,  forming  ethyl  alcohol, 
acetaldehyde,  and  hydrochloric  acid: 

C2H5          H  C2H6OH 


CHa-CHCl    OH       CH3-CH<         =  CH3-CHO+HC1. 

Monochloroether 

Compounds  containing  halogen  and  hydroxyl  in  union  with 
different  carbon  atoms  are  obtained  from  the  polyhydric  alcohols 
by  partial  exchange  of  hydroxyl  for  halogen,  and  have  the  general 
name  halogen-hydrins.  Glycerol  dichlorohydrin,  CsH^OEK^,  is 
formed  when  a  solution  of  glycerol  in  glacial  acetic  acid  is  saturated 
with  hydrochloric-acid  gas.  It  has  the  symmetrical  formula 

CH2C1-CHOH.CH2C1, 

since  it  differs  from  the  dichlorohydrin  obtained  by  addition  of 
chlorine  to  allyl  alcohol,  this  having  the  constitution 

CH2OH.CHC1-CH2C1. 

On  treatment  of  both  dichlorohydrins   with  caustic  potash,  epi- 
chlorohydrin, 

CH2.CH-CH2C1, 


is  obtained. 

Dinitro-compounds  with  both  nitro-groups  in  union  with  the 
same  carbon  atom  are  formed  from  primary  bromo-nitro-com- 
pounds  by  the  action  of  potassium  nitrite: 

CH3.CHBrN02+KN02  =  CH3-CH(NO2)2+KBr. 


196  ORGANIC  CHEMISTRY.  [§§159,160 

The  hydrogen  atom  belonging  to  the^  carbon  atom  carrying 
the  nitro-groups  can  be  readily  replaced  by  metals,  so  that 
these  primary  dinitro-compounds  have  an  acidic  character 
(322). 

159.  Diamines  with  the  two  amino-groups  attached  to  the 
same  carbon  atom  are  not  numerous:    most  of  them  have  their 
amino-groups  in  union  with  different  carbon  atoms.  Some  of  these 
compounds  are  formed  by  the  putrefaction  of  animal  matter,  such 
,as  flesh,  and  are  classed  as  ptomaines  with  other  basic  substances 
similarly  formed.     Such  are  cadaverine  (pentamethylenediamine), 
NH2-CH2- (CH2)3-CH2'NH2,    and   putrescine    (tetramethylenedia- 
mine),  NH2-CH2- (CH2)2.CH2.XH2.     The  constitution  of  these 
substances  has  been  proved  by  synthesis,  pentamethylenediamine 
being  thus  obtained.   Trimethylene  bromide,  Br'CH2»CH2«CH2«Br, 
is  converted  by  treatment  with  potassium  cyanide  into  trimethylene 
cyanide,  CN-CH2-CH2-CH2-CN.     This  substance  is  reduced  with 
sodium  and  boiling  alcohol,  which  converts  the  CN-groups  into 
'CH2NH2-groups  (78),  with  formation  of  the  diamine: 

CN  CH2NH2 

(CH2)3  ->  (CH2)3     . 

CN  CH2NH2 

When  pentamethylenediamine  hydrochloride  is  heated,  it  loses 
one  molecule  of  ammonia,  and  is  converted  into  piperidine,  which 
has  the  character  of  a  saturated  secondary  amine.  For  this  and 
other  reasons  (388)  it  is  assigned  a  ring  or  cyclic  formula: 

,CH2 .  CH2NH2  ,CH2  •  CH2 

CH2  -NH3  =  CH2          ^>NH. 

^CHg  .CH2NH2  \CH2  •  CH2 

Pentamethylenediamine  Piperidine 

When  heated,  tetramethylenediamine  and  trimethylenediamine 
yield  analogous  cyclic  compounds,  but  less  readily,  whereas  ethylene- 
diamine  does  not. 

160.  A  substance,  partly  amine    and    partly  alcohol,  should 
be  mentioned  on  account  of  its  physiological   importance:   it  is 
choline,  CsH15O2N,  which  is  widely  distributed  in  the  vegetable 
kingdom.     Its  constitution  is  inferred  from  its  synthesis  by  the 


§  160]  CHOL1NE  AND  LECITHIN.  197 

interaction    of   trimethylamine    and    ethylene    oxide  in  aqueous- 
solution: 

(CH3)3N  +CH2-CH2  /CH2.CH2OH 

+        \/       =  (CH3)3N 
OHH         O  \OH 

Choline 

Ethylene  oxide  can  also  combine  with  substances  like  ethyl- 
amine,  with  formation  of  amino-alcohols. 

Choline  is  a  constituent  of  a  very  complicated  compound. 
lecithin,  present  in  brain-substance,  yolk  of  egg,  many  seeds,  and 
elsewhere.  It  is  glycerophosphoric  acid  in  which  the  alcoholic 
hydroxyl-groups  are  esterified  by  palmitic,  stearic,  and  oleic  acid; 
and  the  acidic  hydroxyl-groups  are  combined  with  choline.  Various- 
lecithins  are  known:  some  of  them  probably  contain  more  than  one 
kind  of  acid-residue  in  the  molecule.  The  native  lecithins  are  always, 
mixtures. 

On  treatment  with  baryta-water,  lecithin  yields  choline,  one  or 
more  of  the  tatty  acids  named  above,  and  glycerophosphoric  acid*. 
This  acid  is  optically  active,  and  has  the  formula 

CH2OH 

H— C— OH 
I 
CH2-O— PO(OH)2, 

the  central  C-atom  being  asymmetric. 

Lecithin,  likewise,  is  optically  active,  and  may  have  the  formula 

CH2OR 

I 

CHOR' 

I          /-ou 

CH2.0— P:0 

\0— CH2.CH2.N(CH3)3.OH, 

R  and  R'  being  similar  or  dissimilar  acid-radicals. 

The  lecithins  dissolve  readily  in  alcohol,  but  with  difficulty  in- 
ether.  As  the  structural  formula  indicates,  they  yield  salts  with 
both  bases  and  acids. 


POLYBASIC  ACIDS. 


I.  SATURATED   DIBASIC  ACIDS,  CnH2n-204. 

161.  Many  isomerides  of  the  acids  CnH2n(COOH)2  are  theoretic- 
ally possible,  and  differ  from  one  another  in  the  positions  at  which 
the  carboxyl-groups  are  linked  to  the  carbon  chain.  For  many 
reasons,  the  most  important  are  those  with  carboxyl-groups  attached 
to  the  terminal  carbon  atoms  of  the  normal  chain,  the  aa  '-acids 


The  general  methods  for  the  preparation  of  the  dibasic  acids 
and  the  monobasic  acids  are  analogous.  The  former  are  produced 
by  the  oxidation  of  the  corresponding  glycols  and  aldehydes,  and 
by  the  hydrolysis  of  the  dinitriles,  although  many  of  them  are  pre- 
pared by  special  methods. 

Physical  and  Chemical  Properties. 

These  acids  are  well-defined  crystalline  substances:  those 
with  more  than  three  carbon  atoms  can  be  distilled  in  vacuo  with- 
out decomposition.  When  distilled  under  ordinary  pressure, 
many  of  them  lose  water. 

The  melting-points  of  these  acids  exhibit  the  same  peculiarity 
as  those  of  the  fatty  acids  (80)  :  the  members  with  an  even  number 
of  carbon  atoms  have  higher  melting-points  than  those  immediately 
succeeding  them,  with  an  uneven  number  of  carbon  atoms,  as  is 
seen  from  the  table  on  next  page. 

This  relation  is  graphically  represented  in  Fig.  32,  which  indi- 
cates that  the  melting-points  of  the  even  and  uneven  series  approxi- 
mate more  and  more  closely  as  the  number  of  the  carbon  atoms 
increases. 

A  similar  peculiarity  is  displayed  by  other  physical  constants 
of  these  acids,  that  of  the  solubility  in  water  being  given  in  the  last 

198 


161] 


SATURATED  DIBASIC  ACIDS,  CnH2n-2O4. 


199 


column  of  the  table.  The  solubility  of  the  acids  with  an  uneven 
number  of  carbon  atoms  is  much  greater  than  the  solubility  of 
those  with  an  even  number,  and  for  both  it  diminishes  with  increase 
in  the  number  of  carbon  atoms. 


Name. 

Formula. 

Melting- 
point. 

Parts  by 
Weight  Solu- 
ble in  100 
Parts  of 
Water  at  20°. 

Oxalic  acid  

COOH.COOH 

189.5°* 

8»6 

Malonic  acid  

COOH  -CH2-  COOH 

133° 

73-5 

Succinic  acid  

COOH.  (CH<>)2.  COOH 

183° 

5-8 

Glutaric  acid  

COOH.  (CH2)3-  COOH 

97-5° 

63.9 

Adipic  acid  

COOH  .  (CH2)  4  •  COOH 

153° 

.  1»5 

Pimelic  acid  
Suberic  acid  
Azelaiic  acid  

COOH.  (CH2)  5-  COOH 
COOH.  (CH2)e-  COOH 
COOH.  (CH2)7.  COOH 

105.5° 
140° 
108° 

5-0      - 
0-16   - 
0«24 

Sebacic  acid 

COOH  •  (CH2)8.COOH 

134*5° 

0.10  ' 

Nonanedicarboxylic  acid.  .  . 
Decamethylenedicarboxylic 
acid            ... 

COOH.  (CH2)9-  COOH 
COOH  .  (CH2)io  •  COOH 

110° 
126° 

Brassylic  acid  . 

COOH  .  (CH8)n  .COOH 

112° 

Dodecamethylenedicar- 
boxylic  acid  

COOH.  (CH2)12.  COOH 

124° 

*  Anhydrous  oxalic  acid. 


Oxalic  acid  is  a  very  much  stronger  acid  than  its  homologues, 
as  the  dissociation-constants  indicate.     For  oxalic   acid    Wk  is 


FIG.  32. — GUAPHIC  REPRESENTATION  OF  THE  MELTING-POINTS  OF  THE 
ACIDS  CnH2n-2O4. 

about  1000,  for  malonic  acid  16-3,  and  for  succinic  acid  0-65:  for 
the  remaining  acids  it  has  values  which  diminish  with  increase  in 


200  ORGANIC  CHEMISTRY.  [§  162 

the  number  of  carbon  atoms,  but  are  of  the  same  order  as  the  last 
number.  The  longer  the  carbon  chain  between  the  carboxyl- 
groups,  the  weaker  is  the  acid  (172), 

Oxalic  Acid,  C2H2O4,2H2O. 

162.  Between  oxalic  acid  and  formic  acid  there  exists  a  genetic 
interdependence:  it  is  possible  to  prepare  formic  acid  from  oxalic, 
or  conversely,  oxalic  from  formic  acid.  On  rapidly  heating  potas- 
sium or  sodium  formate,  hydrogen  is  evolved  from  the  fusing, 
mass,  and  potassium  or  sodium  oxalate  is  produced : 


KOOCfH 
KOOCH 


KOOC 
KOOC 


H2. 


The  reverse  transformation  of  oxalic  acid  into  formic  acid  has 
already  been  described  (153),  and  constitutes  the  ordinary  method 
for  the  preparation  of  formic  acid. 

Oxalic  acid  frequently  results  in  the  oxidation  of  organic  sub- 
stances with  nitric  acid:  thus,  it  is  formed  by  the  action  of  this 
acid  on  sugar.  It  is  prepared  on  the  manufacturing  scale  by  heat- 
ing a  mixture  of  caustic  potash  and  caustic  soda  to  the  point  of 
fusion  along  with  sawdust.  A  formate  is  an  intermediate  pro- 
duct, and  on  further  heating  loses  hydrogen,  being  converted  into 
an  oxalate.  After  cooling,  the  mass  is  lixiviated  with  water,  the 
oxalate  going  into  solution:  the  oxalic  acid  is  then  precipitated 
as  calcium  oxalate  by  the  addition  of  milk  of  lime,  and  finally 
obtained  in  the  free  state  by  the  action  of  sulphuric  acid. 

The  production  of  this  acid  by  the  interaction  of  carbon  dioxide 
and  potassium  or  sodium  at  about  360°,  and  its  formation  by  the 
hydrolysis  of  cyanogen,  CN-CN,  are  of  theoretical  importance. 

Oxalic  acid  occurs  in  nature  in  different  plants,  chiefly  in 
species  of  oxalis,  in  the  form  of  potassium  hydrogen,  or  calcium, 
salt.  It  is  sometimes  found  as  a  crystalline  deposit  of  calcium 
oxalate,  called  r aphides,  in  plant-cells.  It  crystallizes  with  two 
molecules  of  water  of  crystallization,  which  it  begins  to  lose  at 
30°.  On  careful  heating  the  anhydrous  acid  sublimes,  but  when 
strongly  heated,  either  alone  or  with  concentrated  sulphuric  acid, 
it  decomposes  into  C02,  CO,  and  H2O.  The  velocity  of  this 
decomposition  is  largely  dependent  on  small  differences  in  the 


162] 


OXALIC  ACID. 


201 


amount  of  water  present  in  the  samples  of  concentrated  acid 
employed,  one  of  the  few  instances  of  a  reaction  being  retarded 
by  the  influence  of  water.  A  similar  decomposition  ensues  when 
a  solution  of  uranium  oxalate  is  exposed  to  sunlight,  CO  and  CO2 
Toeing  energetically  evolved.  Oxalic  acid  is  very  readily  oxidized :  a 
volumetric  method  for  its  estimation  depends  upon  the  use  of 
potassium  permanganate  in  sulphuric-acid  solution,  each  molecule 
-of  oxalic  acid  requiring  one  atom  of  oxygen : 

C2H2O44-O  =  2CO2+H2O. 

The  oxidation  with  permanganate  accords  with  the  equation 
2KMnO4  +5C2H2O4  +3H2SO4  =K2SO4  +2MnSO4  +  10CO2  4-8H2O. 

The  manganese  sulphate  formed  has  a  catalytic  accelerating  action 
on  the  process,  so  that,  although  the  first  few  drops  of  permanganate 
solution  are  very  slowly  decolorized,  after  further  addition  of  per- 
manganate the  disappearance  of  the  colour  is  instantaneous.  When 
manganese  sulphate  is  added  to  the  oxalic-acid  solution  before  the 
titration,  the  permanganate  is  at  once  decolorized. 

Only  the  salts  of  the  alkali-metals  are  soluble  in  water.  Calcium 
oxalate,  CaC2O4,2aq,  is  insoluble  hi  acetic  acid,  but  soluble  in 
mineral  acids;  its  formation  serves  as  a  test  both  for  calcium  and 
for  oxalic  acid.  As  a  dibasic  acid,  oxalic  acid  yields  both  acid 
and  normal  salts,  and  the  so-called  quadroxalates  are  known — 
compounds  of  one  molecule  of  acid  salt  with  one  molecule  of 
acid:  among  these  is  "salt  of  sorrel,"  KHC2O4,H2C204,2aq. 
A  great  number  of  complex  salts  of  oxalic  acid  are  known:  many 
of  them  contain  alkali-metals,  and  are  soluble  in  water.  They 
.are  employed  in  electro-analysis. 

A  type  of  these  complex  salts  is  potassium  ferrous  oxalate , 
K2Fe(C2O4)2,  which  yields  a  yellow  solution.  This  indicates  the 
presence  of  a  complex  ion,  probably  (Fe(C2O4)?)",  since  ferrous  salts 
are  usually  light-green.  Potassium  ferrous  oxalate  is  a  strong  reduc- 
ing agent :  it  is  employed  for  the  development  of  photographic  plates. 

Potassium  ferric  oxalate,  K3Fe(C2O4)3,  yields  a  green  solution, 
which  must,  therefore,  also  contain  a  complex  ion,  possibly 
(Fe(C204)3)"'.  Its  solution  is  rapidly  reduced  by  sunlight,  in  accord- 
ance with  the  equation 

2K3Fe(C204)3  -  2K2Fe(C2O4)2  +  K2C204-f  2CO2. 


202  ORGANIC  CHEMISTRY.  [§§  163, 164 

This  property  is  made  use  of  in  the  preparation  of  platinotypes. 
The  photographic  negative  is  placed  upon  a  sheet  of  paper  saturated 
with  potassium  ferric  oxalate:  reduction  to  ferrous  salt  only  takes 
place  where  the  light  is  transmitted  through  the  negative,  and  when 
the  paper  is  placed  in  a  solution  of  a  platinum  salt,  the  metal  is  only 
deposited  on  the  parts  coated  with  potassium  ferrous  oxalate. 

EDER'S  solution  has  remarkable  properties.  It  consists  of  a 
mixture  of  two  volumes  of  a  four  per  cent,  solution  of  ammonium 
oxalate,  and  one  volume  of  a  five  per  cent,  solution  of  mercuric 
chloride.  In  the  dark  it  remains  unaltered,  but  under  the  influence 
of  light  it  decomposes  with  precipitation  of  mercurous  chloride: 

2HgCl2  +  (NH4)2C204  =2HgCl  +2C02  +2NH4C1. 

The  decomposition  is  much  accelerated  by  the  presence  of  certain 
fluorescent  substances,  such  as  eosin  (348). 

163.  Dimethyl  oxalate  is  solid,  and  melts  at  54°:  it  is  employed 
in  the  preparation  of  pure  methyl  alcohol.     Diethyl  oxalate  is  a 
liquid.     Both  are  prepared  by  distilling  a  solution  of  anhydrous 
oxalic  acid  in  the  absolute  alcohol. 

Oxalyl  chloride,  COC1-COC1,  is  prepared  by  the  interaction  of 
two  gramme-molecules  of  phosphorus  pentachloride  and  one 
gramme-molecule  of  oxalic  acid.  It  is  a  colourless  liquid,  boils  at 
64°,  arid  at  — 12°  solidifies  to  white  crystals.  When  its  vapour  is 
brought  into  contact  with  steam,  oxalic  acid  and  hydrochloric 
acid  are  formed.  Liquid  water,  however,  converts  it  quantitatively 
into  carbon  dioxide,  carbon  monoxide,  and  hydrochloric  acid. 

Oxamide,  CONH2-CONH2,  is  a  white  solid,  nearly  insoluble  in 
water,  alcohol,  and  ether,  and  is  obtained  as  a  crystalline  precipi- 
tate by  the  addition  of  ammonia  to  a  solution  of  a  dialkyl  oxalate. 
The  monoamides  of  the  dibasic  acids  are  called  amic  acids,  that 
of  oxalic  acid  being  oxamic  acid,  CONH2-COOH.  It  is  a  crystal- 
line compound,  readily  soluble  in  cold  water,  and  insoluble  in 
alcohol. 

Malonic  Acid,  COOH-CH2.COOH. 

164.  The  constitution  of  malonic  acid  is  proved  by  its  synthesis 
from  monochloroacetic  acid.     When  an  aqueous  solution  of  potas- 
sium monochloroacetate  is  boiled  with  potassium  cyanide,  cyano- 


§  164]  MALONIC  ACID.  203 

acetic  acid  is  formed,  and  can  be  converted  into  malonic  acid  by 
hydrolysis  of  the  nitrile-group  : 


PTT   / 

COOH  ~          <  COOH  "  COOH' 

Monochloroacetic  acid      C.vanoacetic  acid  Malonic  acid 

Malonic  acid  is  a  crystalline  substance:  some  of  its  physical 
properties  are  given  in  the  table  in  161.  When  heated  somewhat 
above  its  melting-point,  it  loses  one  molecule  of  carbon  monoxide, 
being  converted  into  acetic  acid: 


COOH.CH2.|COO|H  =  CO2+  COOH-CH3. 

It  is  found  that  when  a  compound  with  two  carboxyl-groups  in  union 
with  one  carbon  atom  is  heated  above  its  melting-point,  its  molecule 
loses  one  molecule  of  carbon  dioxide. 

The  most  important  derivative  of  malonic  acid  is  diethyl  malo- 
nate,  many  important  syntheses  being  accomplished  by  its  aid.  It 
is  a  liquid  of  faint  odour,  boiling  at  198°,  and  having  a  specific 
gravity  of  1-061  at  15°.  On  treatment  with  sodium,  in  the  pro- 
portion of  one  atom  to  each  molecule  of  ester,  hydrogen  is  evolved, 
and  the  diethyl  malonate  converted  into  a  solid  mass.  In  this 
reaction,  hydrogen  is  replaced  by  sodium,  yielding  diethyl  mono- 
sodiomalonate,  a  compound  of  the  structure 

COOC2H5 
CHNa  . 
COOC2H5 

This  is  proved  by  treating  it  with  an  alkyl  halide  (iodide),  a  sodium 
halide  and  an  ester  being  obtained : 

C2H5|I  +NajCH(COOC2H5)2  =  C2H5-CH(COOC2H5)2+NaI. 

On  saponification,  this  ester  yields  a  homologue  of  malonic  acid. 

If  two  atoms  of  sodium,  instead  of  one,  react  with  one  molecule 
of  diethyl  malonate,  two  hydrogen  atoms  are  replaced.  Both  of 
these  hydrogen  atoms  are  in  the  methylene-group,  because,  on 
treatment  of  the  disodio-compound  with  two  molecules  of  an 
alkyl  iodide,  the  two  sodium  atoms  are  replaced  by  alkyl,  with 


204  ORGANIC  CHEMISTRY.  [§  164 

production  of  a  substance  which  on  saponification  is  converted  into 
a  homologue  of  malonic  acid : 

COOC2H5  COOC2H5 

C|Na2+2LlC2H5  =  2NaI+C(C2H5)2  . 
COOC2H5  COOC2H5 

It  is  also  possible  to  introduce  two  different  alkyl-groups  into 
-diethyl  malonate.  Thus,  when  diethyl  monosodiomalonate  is  treated 
with  methyl  iodide,  the  diethyl  ester  of  methylmalonic  acid  is 
formed:  on  treatment  with  sodium  this  again  yields  a  sodio-com- 
pound,  which  is  converted  by  ethyl  iodide  into  the  diethyl  ester 
of  methylethylmalonic  acid.  The  reaction  is  discussed  further 
in  the  chapter  on  tautomerism  (235). 

From  these  examples  it  is  evident  that  it  is  possible  to  synthe- 
size a  great  number  of  dibasic  acids  from  diethyl  malonate.  More- 
over, since  all  these  acids  contain  two  carboxyl-groups  linked  tc 
the  same  carbon  atom,  and  have  in  common  with  malonic  acid  the 
property  of  losing  CO2  when  heated  above  their  melting-points, 
it  is  evident  that  the  so-called  " malonic-ester  synthesis"  is  also 
available  for  the  preparation  of  the  monobasic  fatty  acids.  Thus, 
methylethylmalonic  acid  loses  CO2  on  heating,  yielding  methyl- 
ethylacetic  acid,  identical  in  constitution  with  active  valeric  acid 
(51),  and  resoluble  into  two  active  components: 

COOH  COOH 

CH3.C.C2H5  =  CH3.C.C2H5. 
fDOOJH  H 

Methylethylmalonic  Valeric  acid 

acid 

The  malonic-ester  synthesis  is  much  employed  in  the  prepara- 
tion of  acids,  and  will  be  the  subject  of  frequent  reference. 

Details  of  the  malonic-ester  synthesis. — One  gramme-molecule  of 
diethyl  malonate  is  mixed  with  a  ten  per  cent,  solution  of  sodium 
ethoxide  (1  equivalent)  in  absolute  alcohol,  obtained  by  the  action 
of  sodium  on  alcohol.  To  this  mixture  is  added  one  gramme-mole- 
cule of  an  alkyl  iodide,  and  the  reaction-mixture  heated  on  a  water- 
bath  under  a  reflux-condenser  until  the  liquid  is  no  longer  alkaline. 
After  the  alcohol  has  been  distilled  off,  the  residue  is  treated  wita 


:§§  165, 166]       CARBON  SUBOXIDE  AND  SUCCINIC  ACID.         205 

water  to  dissolve  the  sodium  iodide  formed,  and  the  diethyl  alkyl- 
malonate  extracted  with  ether.  The  ethereal  solution  is  dried  over 
calcium  chloride,  the  ether  distilled,  and  the  residue  purified  by 
fractionation. 

If  it  is  desired  to  introduce  two  alkyl-radicals  or  other  groups, 
two  equivalents  of  sodium  ethoxide  and  two  gramme-molecules  of 
an  alkyl  iodide  are  employed.  When  two  different  groups  are  to  be 
substituted,  one  of  them  is  first  introduced  into  the  molecule,  and 
on  subsequent  treatment  with  a  second  gramme-molecule  of  sodium 
ethoxide  and  of  alkyl  iodide,  the  diethyl  dialkylmalonate  is  produced. 
Otherwise,  the  procedure  is  identical  with  that  described  above. 

165.  Carbon  suboxide,  C3O2,  is  formed  by  the  distillation  of  dry 
malonic  acid  with  ten  times  its  weight  of  phosphoric  oxide: 

CH2  (COOH)  2 =C3O2  +  2H20. 

This  mode  of  formation  indicates  that  carbon  suboxide  has 
the  constitutional  formula 


CO 

It  is  a  gas  of  very  pungent  odour,  which  can  be  condensed  to  a 
liquid  boiling  at  7°.  With  water,  it  regenerates  malonic  acid,  and 
may,  therefore,  be  regarded  as  an  anhydride  of  this  acid.  The 
true  anhydride, 


analogous  to  the  anhydrides  of  the  higher  homologues  of  malonic 
acid,  is  unknown. 


Succinic  Acid,  COOH -CH2.CH2.  COOH. 


166.  Succinic  acid  is  a  crystalline  substance,  melting  at  182°, 
and  dissolving  with  difficulty  in  cold  water.  It  is  present  in 
amber,  in  fossilized  wood,  and  in  many  plants,  and  can  be  syn- 
thetically prepared  by  the  following  methods. 


206  ORGANIC  CHEMISTRY.  [§  166 

1.  From  ethylene  bromide  by  treatment  with  potassium  cya- 
nide, which  converts  it  into  ethylene  cyanide,  CN'CH2'CH2*CN: 
on  hydrolysis,  this  yields  succinic  acid. 

2.  From  malonic  acid  by  treating  diethyl  monosodiomalonate 
with  ethyl  monochloroacetate: 

(COOC2H5)2CH|Na  +Cl]H2C-COOC2H5  = 
+  (COOC2H5)2CH.CH2.COOC2H5. 


In  this  reaction  an  ester  of  ethanetricarboxylic  acid  is  formed; 
and  when  heated  above  its  melting-point,  the  corresponding  acid 
loses  CO2,  yielding  succinic  acid: 

CH2.COOH        CH2.COOH 
p5G|H.CH.COOH      *  CH2.COOH' 

Succinic  acid,  and  symmetrically  substituted  succinic  acids, 
can  also  be  obtained  by  the  action  of  an  ethereal  solution  of  iodine 
or  bromine  upon  diethyl  monosodiomalonate  or  its  monoalkyl- 
derivatives: 

COOC2H5  COOC2H5         COOC2H5    COOC2H5 

A»C|Na        +I2+Na|C-A'         =  A-C—  —  C-A'          +2NaI. 

COOC2H5  COOC2H5         COOC2H5    COOC2H5 

A  =  Hydrogen  or  alkyl  Tetracarboxylic  ester 

By  saponification,  and  elimination  of  CO2,  the  ester  formed  is  con- 
verted into  the  dibasic  acid: 

COOH   COOH 

•  A  -CH.COOH 

A-C—     —  C-A'       =          .  +2CO2, 

A'-  CH-COOH^ 


Unlike  calcium  oxalate,  calcium  succinate  is  soluble  in  water. 
A  characteristic  salt  is  ferric  succinate,  deposited  as  an  amorphous, 
flocculent,  brownish-red  precipitate  by  mixing  solutions  of  ferric 
chloride  and  an  alkali-metal  succinate. 


167]  ELECTRO-SYNTHESIS  OF  DIBASIC  ACIDS.  207 


Electro-synthesis  of  Dibasic  and  Other  Acids. 

167.  When  the  aqueous  solution  of  an  ester-salt  of  a  dibasic 
acid  is  eiectrolyzed,  the  metallic  ion  goes  to  the  cathode,  the  anion 
to  the  anode: 

Anion  Cation 


C2H5O.OC.CH2.COO     K    . 

Ethyl  potassium  malonate 

This  anion,  however,  is  not  stable;  after  being  discharged  at  the 
anode,  it  decomposes  into  carbon  dioxide  and  C2H5OOC»CH2  —  , 
and  two  of  these  residues  unite  to  form  diethyl  succinate: 


By  this  method  it  is  possible  to  synthesize  the  higher  dibasic 
acids  from  the  lower.  A  high  current-density  is  necessary;  that  is, 
the  number  of  amperes  entering  or  leaving  the  electrode  per  square 
centimetre  of  surface.  This  is  attained  by  employing  a  very  small 
anode.  The  concentration  of  the  anions  discharged  at  the  anode 
is  proportional  to  the  current-strength  —  the  number  of  amperes  — 
so  that  with  a  high  current-density  there  is  a  great  number  of  dis- 
charged anions  at  the  anode,  and  these  can  interact  readily. 

This  synthesis  of  dibasic  acids  is  an  extension  of  an  electro- 
synthesis  carried  out  long  ago  by  KOLBE.  He  showed  that  on 
electrolysis  a  solution  of  potassium  acetate  yields  ethane: 


CH3.|COO      K  CH3 

CH3.|COO      K  CH3' 

Anion  Cation 

Many  other  extensions  are  known:  thus,  a  mixture  of  a  salt  of  a 
monobasic  fatty  acid  and  an  ester-salt  yields  at  the  anode  the 
ester  of  a  monobasic  acid : 

CH3.|COO[K  +  KlOOC.|CH2.CH2.COOC2H5-> 

Potassium  acetate  Ethyl  potassium  succinate 

-*  CH3  -  CH2  -  CH2  •  COOC2H5. 

Ethyl  butyrate 


208 


ORGANIC   CHEMISTRY. 


168 


Formation  of  Anhydrides. 

168.  Oxalic  acid  and  malonic  acid  do  not  yield  anhydrides  (165), 
while  succinic  acid,  C4H6O4,  and  glutaric  acid,  C5H8O4,  do  so  very 
readily.  The  formation  of  anhydride  is  due  to  the  elimination  of  one 
molecule  of  water  from  one  molecule  of  the  dibasic  acid,  as  is  proved 
by  a  determination  of  the  molecular  weights  of  the  anhydrides: 


CH2— COOlH 
I  j-1     -H20 

CH9— COOH 


/CH2— COOlH 
CH2  -H20 

\CH2— CO  OH 


CH-z—  OX 


0; 


Succinic  anhydride 

/CH2—  CO\ 
CH2  O. 


FIG.  33. — SPACIAL  REPRESENTATION  OF  THE  BONDS  BETWEEN  2-5 

C-ATOMS. 


§  168]  ANHYDRIDES  OF  DIBASIC  ACIDS.  29'J 

These  anhydrides  are  reconverted  into  the  corresponding  dibasic 
acids  by  dissolving  them  in  water. 

CH2-CO 
A  derivative  of  succinic  acid,  succmimide,   \  /NH,   has 

CH2.COX 

a  ring  of  four  carbon  atoms  and  one  nitrogen  atom:  it  is  formed 
by  the  rapid  distillation  of  ammonium  succinate.  The  atoms  situ- 
ated at  the  extremities  of  a  carbon  chain  of  four  or  five  C-atoms 
interact  very  readily :  those  in  shorter  chains  only  interact  with 
difficulty,  or  not  at  all.  Analogous  phenomena  are  the  elimina- 
tion of  one  molecule  of  water  from  aa'-glycols  (150),  and  of 
ammonia  from  aa'-diamines  (159),  both  very  readily  effected 
from  a  carbon  chain  of  four  or  five  C-atoms,  but  impossible,  or 
leading  to  the  formation  of  very  unstable  compounds,  when  the 
chain  is  shorter.  A  satisfactory  explanation  of  these  phenomena, 
and  others  of  the  same  type,  may  be  attained  by  a  consideration 
of  the  direction  of  the  bonds  in  space.  It  was  assumed  (48) 
that  the  four  affinities  of  the  carbon  atom  are  directed  towards 
the  angles  of  a  regular  tetrahedron  with  the  carbon  atom  at 
the  centre.  For  a  single  bond  between  two  carbon  atoms  it  is 
assumed  that  one  affinity  of  each  of  these  atoms  is  linked  to  one 
affinity  of  the  other  (Fig.  33).  The  position  in  space  of  the  C-atoms 
in  a  chain  of  three  or  more  members,  and  the  direction  of  their 
affinities,  are  represented  in  the  figure. 

It  is  evident  that  in  a  normal  chain  of  four  C-atoms  the  affinities 
at  the  extremities  approach  one  another  closely,  and  in  a  chain  of 
five  C-atoms  still  more  closely,  so  that  they  can  interact  readily. 

A  few  instances  of  compounds  with  a  closed  chain  containing 

Gri2*Cri2 
only  two  C-atoms,  such  as  ethylene  oxide,   \/       ,  are  known. 

O 

The  figure  indicates  that  for  two  C-atoms  the  direction  of  the  affin- 
ities must  undergo  a  considerable  change  to  render  the  formation  of 
a  ring  possible.  Such  compounds  are  unstable,  the  closed  chain 
being  very  readily  opened,  as  is  indicated  by  the  "strain-theory" 
of  VON  BAEYER  (120). 


210  ORGANIC  CHEMISTRY.  [§  169 

II.  UNSATURATED    DIBASIC  ACIDS. 
Fumaric  Acid  and  Maleic  Acid,  C4H404. 

i6g.  The  most  important  members  of  the  group  of  unsaturated 
dibasic  acids  are  fumaric  acid  and  maleic  acid,  both  with  the  formula 
C4H4O4.  They  have  been  much  investigated,  a  complete  explana- 
tion of  their  isomerism  having  been  finally  arrived  at  by  an  appli- 
cation of  the  principles  of  stereoisomerism. 

Fumaric  acid  is  somewhat  widely  distributed  in  the  vegetable 
kingdom.  It  does  not  melt  at  the  ordinary  pressure,  but  sub- 
limes at  about  200°:  it  dissolves  with  difficulty  in  water.  Maleic 
acid  is  not  a  natural  product:  it  melts  at  130°,  and  is  very  readily 
soluble  in  water. 

Both  acids  can  be  obtained  by  heating  malic  acid  (187), 

COOH  -  CHOH  •  CH2  •  COOH, 

the  result  depending  on  the  temperature  and  duration  of  the  reac- 
tion. Fumaric  acid  is  the  principal  product  when  the  temperature 
is  maintained  at  140°-150°  for  a  long  time,  but  when  a  higher  tem- 
perature is  employed,  and  the  heating  is  quickly  carried  out,  the 
anhydride  of  maleic  acid  distils  along  with  water.  This  anhydride 
readily  takes  up  water,  regenerating  the  acid.  This  is  the  ordinary 
method  for  the  preparation  of  these  acids,  and  it  indicates  that 
both  have  the  same  structural  formula: 

COOH.CH.CH-COOH-H2O  =  COOH.CH:CH.COOH. 
|OHH| 

This  view  of  their  constitution  is  supported  by  the  fact  that  on 
treatment  with  sodium-amalgam  and  water  both  acids  yield  suc- 
cinic  acid,  and  also  by  the  formation  of  monobromosuccinic  acid  by 
addition  of  HBr,  and  of  malic  acid  by  heating  with  water  at  a  high 
temperature.  Both  acids  have  therefore  the  same  constitutional 
formula, 

COOH- CHiCH- COOH. 

The  isomerism  of  the  crotonic  acids  is  similar  (136).  It  remains 
to  consider  how  this  isomerism  can  be  explained  by  the  aid  of 
stereochemistry. 


169] 


FVMARIC  ACID  AND  MALE  1C  ACID. 


211 


A  single  bond  between  two  carbon  atoms  may  be  represented 
as  in  Fig.  34  (168).     If  the  tetrahedra  are  drawn  in  full,  then  the 


FIG.  34.  FIG.  35. 

SINGLE  BOND  BETWEEN  TWO  CARBON  ATOMS. 

single  bond  will  be  as  in  Fig.  35.  If  the  tetrahedra  are  free  to  rotate 
round  their  common  axis,  isomerism  cannot  be  expected  for  com- 
pounds Cabc — Cdef,  nor  has  it  ever  been  observed. 


\ 


FIG.  36.  FIG.  37.  FIG.  38. 

GRAPHIC  SPACIAL  REPRESENTATION  OF  THE  DOUBLE  BOND  BETWEEN 
TWO  CARBON  ATOMS. 

When  a  double  bond  is  present,  then  two  affinities  of  each 
carbon  atom  come  into  play,  as  graphically  represented  in  Figs. 
36,  37,  and  38.  Free  rotation  of  the  tetrahedra  relative  to  one 
another  is  then  no  longer  possible. 

The  figures  indicate  that  difference  of  grouping  depends  on  the 
position  of  the  groups  a  and  b  of  one  tetrahedron  .with  reference  to 


212  ORGANIC  CHEMISTRY.  [§  170 

the  similar  groups  a  and  b  of  the  other,  a  may  be  over  a,  and  b 
over  b,  as  in  Fig.  37 :  or  a  may  be  over  b,  and  b  over  a,  as  in  Fig.  38w 
This  can  be  represented  by  the  formulae 

a— C— b  a—C—b 

II  and  ||      . 

a— C— b  b—C—a 

Thus,  the  two  crotonic  acids  would  be 

CH3— C— H  H— C— OH3 

II  and  || 

H— C— COOH  H— C— COOH 

Trans  Cis 

and  fumaric  and  maleic  acids  would  have  the  formulae 

COOH— C— H  H— C— COOH 

I.  and     II. 

H— C— COOH  H— C— COOH 

Trans  Cis 

It  must  now  be  proved  which  of  these  two  formula?  belongs  to 
fumaric  acid,  and  which  to  maleic  acid. 

Maleic  acid  yields  an  anhydride,  while  fumaric  acid  does  not. 
In  formula  II.  the  carboxyl-groups  are  in  juxtaposition  to  one 
another,  but  in  formula  I.  they  are  as  far  removed  from  each  other 
as  possible.  Only  in  the  acid  with  the  cis-formula  are  the  carboxyl- 
groups  represented  in  a  position  to  interact  readily : 

H— C— COOIH  H— C— CO 

II      r     -»       II    >o. 
H—C— colon        H— c— co 

Maleic  acid  Maleic  anhydride 

From  this  it  is  inferred  that  fumaric  acid  has  the  constitution  indi- 
cated in  formula  L,  and  maleic  acid  that  in  formula  II. 

170.  Further  consideration  indicates  that  this  view  also  accounts 
for  the  other  known  properties  of  these  acids.  Neither  formula 
contains  an  asymmetric  C-atom,  so  that  neither  optical  activity  nor 
the  great  resemblance  in  such  properties  as  specific  gravity,  melting- 
point,  solubility,  etc.,  due  to  the  similarity  in  internal  structure 
characteristic  of  the  isomerism  occasioned  by  an  asymmetric  carbon: 
atom,  is  to  be  expected.  Fumaric  acid  and  maleic  acid  do,  in  fact, 
display  great  differences  in  these  physical  properties. 


170] 


FUMARIC  ACID  AND  MALEIC  ACID. 


213 


Both  fumaric  acid  and  malei'c  acid  combine  with  bromine,  but 
the  dibromo-addition-products  thus  obtained  are  different.  Fu- 
maric acid  yields  dibromosuccinic  acid,  soluble  with  difficulty  in 
water;  and  maleic  acid  isodibromosuccinic  acid,  much  more  readily 
soluble  in  water.  Figs.  39  to  42  indicate  that  different  acids  must 
result  from  this  reaction.  Figs.  40  and  42,  representing  dibromo- 


HO-OC 


HO-OC 


2Br  = 


CO'OH 

FIG.  39. — FUMARIC  ACID. 
COOHv 


CO-OH 


FIG.  40. — DIBROMOSUCCINIC  ACID. 


-h  2Br 


CO-OH 


FIG.  41. — MALEIC  ACID. 


CO-OH 


FIG.  42. — tsoDiBROMOSucciNic  ACID. 


acid  and  isodibromosuccinic  acid  respectively,  cannot  be 
made  to  coincide  by  rotation;  and  this  is  made  more  evident  by 
-comparing  Figs.  42  and  43.  The  latter  is  obtained  from  Fig.  40  by 
rotation  of  the  upper  tetrahedron  round  the  vertical  axis,  the  posi- 
tion of  the  lower  tetrahedron  remaining  unaltered.  In  the  figures 
the  order  of  the  groups  linked  to  both  carbon  atoms  of  the  iso-acid 
is  H,  Br,  COOH  from  left  to  right:  for  the  lower  carbon  atom  of 


214 


ORGANIC  CHEMISTRY. 


[§170 


dibromosuccinic  acid  (Fig.  40)  the  order  is  similar,  but  for  the  upper 
carbon  atom  it  is  from  right  to  left. 

When  HBr  is  removed  from  dibromosuccinic  acid  (Fig.  43),  the 
H-atom  linked  to  one  carbon  atom  and  the  Br-atom  linked  to  the 
other  are  eliminated,  yielding  an  acid  COOH-CHrCBr-COOH. 
This  removal  of  HBr  could  not  be  effected  if  the  tetrahedra  were 


CO-OH 


—  HBr  = 


CO-OH 


FIG.  43. — DIBROMOSUCCINIC  ACID. 


CO-OH 


CO-OH 


FIG.  44. — BROMOMALEIC  ACID. 


HO-OC 


CO-OH 


CO-OH 

Br  Br 

FIG.  45. — iso DIBROMOSUCCINIC  ACID.  FIG.  46. — BROMOFUMARIC  ACID. 


in  the  position  shown  in  Fig.  40:  rotation  round  the  vertical  axis 
is  essential  to  bring  H  and  Br  into  " corresponding''  positions,  as 
in  Fig.  43:  elimination  of  HBr  produces  the  acid  represented  in 
fig.  44.  This  acid  readily  yields  an  anhydride,  since  the  COOH- 
groups  are  in  the  corresponding  positions:  it  is  therefore  bromo- 
maleic  acid. 


§§171,172]        FUMARIC  ACID  AND  MALElC  ACID.  215 

When  HBr  is  removed  from  isodibromosuccinic  acid,  repre- 
sented in  Fig.  45  (obtainable  from  Fig.  42  by  rotation  in  the  same 
way  as  Fig.  43  from  Fig.  40),  an  acid  results  which  does  not 
yield  a  corresponding  anhydride,  but  is  converted  by  elimination 
of  water  into  the  anhydride  of  bromomaleiic  acid.  This  behaviour 
resembles  that  of  fumaric  acid,  which  under  the  same  conditions 
yields  malei'c  anhydride.  This  acid  must  therefore  be  bromo- 
Jumaric  acid  (Fig.  46). 

It  follows  that  the  constitution  assumed  for  these  acids  on 
stereochemical  grounds  accounts  for  their  chemical  properties. 
Another  example  which  also  supports  this  explanation  is  men- 
tioned in  194. 

171.  Malei'c  acid  can  be  converted  into  fumaric  acid  by  keeping 
it  for  some  time  at  a  temperature  above  its  melting-point;    by 
bringing  it  into  contact  with  hydrogen  halides  at  ordinary  tem- 
peratures;  by  exposing  its  concentrated  solution  in  presence  of  a 
trace  of  bromine  to  the  action  of  sunlight,  a  slow  reaction  in 
absence  of  light;  by  treating  ethyl  maleate  with  small  quantities 
of  iodine;    or  by  other  means.     The  facility  of  all  these  decom- 
positions indicates  that  malei'c  acid  is  the  unstable,  and  fumaric 
acid  the  stable,   modification.     Inversely,  fumaric   acid  is   con- 
verted by  distillation  into  malei'c  anhydride.     Fumaric  acid  is 
also  converted  into  malei'c  acid  by  the  action  of  ultraviolet  light. 

Affinity-constants  of  the  Unsaturated  Acids. 

172.  Like  the  monobasic  unsaturated  acids  (135),  the  dibasic 
unsaturated  acids  have  greater  affinity-constants  than  the  corre- 
sponding saturated  acids.      For  succinic  acid,  104fc  =0*665,  and 
for  fumaric   acid,    104fc=9-3.     The   strength  of  acetylenedicar- 
boxylic  acid,  COOH -0=0 -COOK  (obtained  by  the  interaction  of 
alcoholic  potash  and  dibromosuccinic  acid, 

COOH-CHBr— CHBr-COOH), 

is  about  equal  to  that  of  sulphuric  acid.  Thus  the  presence  of 
a  double  bond,  and  even  more  of  a  triple  bond,  intensifies  the  acidic 
character.  For  maleic  acid  104&  =  117,  or  about  twelve  times  as 


216  ORGANIC  CHEMISTRY.  [§173 

much  as  for  fumaric  acid.  This  indicates  the  great  influence 
exerted  by  the  distance  between  the  carboxyl-groups  in  the  mole- 
cule upon  the  strength  of  these  acids. 

The  ionization  of  dibasic  acids  is  a  step-by-step  process.  An 
acid  H2A  first  yields  H  +  HA',  and  then  on  further  dilution  HA'  is 

ionized  to  H  -f  A".  In  this  dissociation  remarkable  differences  have 
been  observed.  For  some  acids  the  second  stage  of  ionization  does 
not  begin  until  the  first  is  almost  complete,  but  for  other  acids  it  is 
already  begun  when  about  half  of  the  first  stage  is  over.  The  degree 
of  ionization  depends  upon  the  relative  position  of  the  carboxyl- 
groups  in  the  molecule.  The  nearer  these  groups  are  to  each  other, 
the  more  extended  is  the  first,  and  the  smaller  the  second,  stage  of 
ionization;  and  vice-versa. 

This  phenomenon  is  readily  explained  by  assuming  that  the  nega- 
tive charge  of  the  anion  is  concentrated  on  the  hydroxyl-oxygen  of  the 
ionized  carboxyl-group.  During  the  ionization  of  the  first  H-atom, 
the  presence  of  one  carboxyl-group  promotes  the  ionization  of  the 
other.  This  influence  is  greatest  when  the  carboxyl-groups  are 
<;lose  together.  Other  negative  groups  produce  a  similar  effect  (178 
and  183).  When,  however,  the  ionization  of  the  first  H-atom  is 
•complete,  the  HA'-residue  is  decomposed  with  difficulty  into  H  and 
A",  on  account  of  the  attraction  exerted  by  the  negative  charge  of 
this  residue  on  any  positively-charged  H-ion  liberated,  this  attraction 
being  greatest  when  the  negative  charge  is  close  to  the  H-atom  of 
the  HA'-residue.  On  the  assumption  that  this  charge  is  situated 
on  the  hydroxyl-oxygen  of  the  first  carboxyl-group,  its  attraction  is 
greatest  when  the  two  carboxyl-groups  in  the  non-ionized  acid  are 
in  close  proximity.  When,  however,  the  H-atom  of  the  first  car- 
boxyl-group and  the  negatively-charged  hydroxyl-oxygen  of  the 
HA'-residue  are  further  apart,  the  second  stage  of  the  ionization 
meets  with  less  resistance,  and  therefore  takes  place  more  readily. 

Dibasic  Acids  with  more  than  one  Triple  Bond. 

173.  VON  BAEYER  has  prepared  dibasic  acids  containing  more  than 
one  triple  bond  in  the  molecule,  from  acetylenedicarboxylic  acid. 
When  heated  with  water,  its  potassium  hydrogen  salt  is  converted 
into  potassium  propiolate  (139),  with  loss  of  C02: 

=  C02+KOOC.C=CH. 


§174]  POLY  BASIC  ACIDS.  217 

When  the  copper  derivative  of  this  salt,  KOOC-CEECcu,*  is  treated 
with  potassium  ferricyanide  in  alkaline  solution,  CuO  is  formed,  while 
the  two  acid-residues  simultaneously  unite  with  production  of  the 
potassium  salt  of  diacetylenedicarboxylic  acid, 

KOOC  .C=C—  C=C  -COOK. 

The  potassium  hydrogen  salt  of  this  acid  also  loses  C02  readily, 
and  the  coppor  derivative  of  the  monobasic  acid  thus  formed  is 
converted  by  similar  oxidation  into  CuO  and  the  potassium  salt  of 
tetra-acetylenedicarboxylic  acid  : 


These  compounds  are  very  unstable,  being  decomposed  by  the  action 
of  light,  and  otherwise. 

III.  POLYBASIC  ACIDS. 

174.  Acids  with  three  carboxyl-groups  in  union  with  one  car- 
bon atom  are  unknown,  except  as  esters.  The  triethyl  ester  of 
methanetricarboxylic  acid  is  obtained  by  the  action  of  ethyl  chloro- 
carbonate  (263)  on  diethyl  monosodiomalonate: 

C2H5OOC|ClTN^CH(COOC2H5)2  =  C2H5OOC.CH(COOC2H5)2. 

Ethyl  chlorocarbonate 

When  this  ester  is  saponified,  CO2  is  simultaneously  eliminated, 
malonic  acid  being  formed  instead  of  the  corresponding  tribasic 
acid.  This  is  another  instance  of  the  phenomenon  that  several 
negative  groups  do  not  remain  in  union  with  one  carbon  atom,  two 
being  the  maximum  number  for  carboxyl  (149  and  177). 

A  description  of  the  syntheses  of  a  few  of  the  polybasic  acids 
will  afford  examples  of  the  methods  adopted  for  the  preparation 
of  compounds  of  this  class. 

A  type  of  the  'tribasic  acids  is  afia'-propanetricarboxylic 
acid,  or  tricarballylic  acid,  obtainable  by  several  methods. 

1.  From  tribromohydrin  by  treatment  with  potassium  cyanide, 
and  hydrolysis  of  the  tricyanohydrin  thus  formed: 

CH2—  CH—  CH2       CH2—  CH—  CH2       CH2  --  CH  --  CH2 
Br       Br      Br          CN      CN     CN  "  >  COOH    COOH   COOH. 


218  ORGANIC  CHEMISTRY.  [§  174 

2.  From  diethyl  disodiomalonate  and  ethyl  monochloroacetate: 


(C2H5OOC)2C  [Ka2  +  2C1  |CH2 

C2H5OOC    r    CH2.COOC2H5 
C2H5OOC>1  <CH2.COOC2H5 

On  saponification  of  this  ester,  an  acid  is  obtained  which  on 
heating  loses  C02,  with  formation  of  tricarballylic  acid: 

CH2.COOH  CH2.COOH 

-*  6H-COOH- 

CH2.COOH  CH2-COOH 

A  synthesis  poculiar  to  the  polybasic  acids  consists  in  the 
addition  of  ethyl  monosodiomalonate  to  the  esters  of  unsaturated 
acids,  such  as  fumaric  acid: 

NaCH.COOC2H5 
Na  CH.COOC2H5 

I  +||  =       CH.COOC2H5 

HC(COOC2H5)2    CH.COOC2H5  | 

CH(COOC2H5)2 

Saponification,  with  subsequent  elimination  of  C02,  yields  tricar- 
ballylic acid.     It  melts  at  166°,  and  dissolves  readily  in  water. 

Aconitic  acid,  melts  at  191°:  it  is  a  type  of  the  unsaturated 
tribasic  acids.  It  is  obtained  from  citric  acid  (197)  through 
removal  of  water  by  heating.  The  constitution  of  aconitic  acid  is 


COOH  COOH  COOH 

for  on  reduction  it  is  converted  into  tricarballylic  acid. 


SUBSTITUTED  ACIDS. 


I.  HALOGEN-SUBSTITUTED  ACIDS. 

175.  The  halogen-substituted    acids   can   be    obtained  by  the 
direct  action  of  chlorine  or  bromine  upon  the  saturated  fatty 
acids,  but  this  process  is  not  very  satisfactory.     The  monochloro- 
acids  and  monobro mo-acids  are  best  prepared  by  the  action  of 
chlorine  or  bromine,  not  upon  the  acid,  but  upon  its  chloride  or 
bromide.     The  process  involves  treating  the  acid  with  phosphorus 
and  a  halogen,  the  phosphorus  halide  produced  reacting  with  the 
acid  to  form  an  acid  chloride  or  bromide,  R-COX,  which  is  then 
attacked  by  the  excess  of  halogen  present. 

Some  acids  cannot  be  thus  brominated:  such  are  trimethyl- 
acetic  acid,  (CH3)3C-COOH,  and  tetramethylsuccinic  acid, 

(CH3)2C.COOH 

.     In  these  acids  there  is  no  hydrogen  in  union 
(CH3)2C.COOH 

with  the  a-carbon  atom,  which  is  directly  linked  to  carboxyl. 
As  a  general  rule,  it  is  only  possible  to  brominate  acids  of  which 
the  a-carbon  atom  is  linked  to  hydrogen,  the  acids  formed  being 
called  a-bromo-acids.  The  constitution  of  these  is  proved  by 
converting  them  into  hydro xy-ac ids  (179),  which  are  shown  to  be 
a-compounds  through  their  synthesis  by  another  method. 

Halogen-substituted  acids  can  also  be  prepared  by  addition  of 
hydrogen  halide  or  halogen  to  the  unsaturated  acids,  or  by  the 
action  of  phosphorus  halides  on  the  hydroxy-acids.  The  iodo- 
acids  can  sometimes  be  advantageously  obtained  from  the  corre- 
sponding chloro-derivatives  by  heating  them  with  potassium  iodide. 

176.  The  introduction  of  halogen  into  the  molecule  causes  a 
marked   increase  in   the  strength   of   an    acid,  as   will  be  seen 
from    the   table   on  next  page  of  dissociation-constants,   104&. 
This  table  indicates  that  the  strength  of  an  acid  is  increased  to  a 
greater  extent  by  chlorine  than  by  bromine,  and  by  bromine  than. 

219 


220 


ORGANIC   CHEMISTRY. 


[§  176 


Name. 

Formula. 

lO'fc. 

Acetic  acid  

CH3.CO2H 

0-18 

Monochloroacetic  acid  .  .    . 

CH2C1.CO2H 

15-5 

Monobrbmoacetic  acid  

CH2Br.CO2H 

13.8 

Monoiodoacetic  acid  .  

CHJ.CO2H 

7«5 

Dichloroacetic  acid  
Trichloroacetic  acid  

CHC12.C02H 
CC1,.CO2H 

514 
12100 

Butyric  acid  

CH.  .  CH2  •  CH2  •  CO2H 

0-152 

a-Chlorobutyric  acid  

CH  ,  •  CH2  .  CHC1  .  CO2H 

13.  9V 

@-Chlorobutyric  acid  

CH3  •  CHC1-  CHo  •  CO2H 

0.89 

•y-Chlorobutyric  acid 

CH2C1  -  CH2  -  CH2  •  CO2H 

0*3  (ca  ) 

by  iodine,  and  that  a  marked  increase  is  occasioned  by  the  intro- 
duction of  more  than  one  chlorine  atom.  The  position  of  the  halo- 
gen atom  also  exerts  an  influence:  for  iodoacetic  acid  with  the 
I-atom  in  the  ^-position  the  value  of  the  constant  is  32  times  as 
great  as  for  acetic  acid,  while  for  /?-iodopropionic  acid  104&  is  only 
7  times  as  great  as  for  propionic  acid. 

The  influence  of  the  carboxyl-groups  upon  the  halogen 
atoms  is  such  that  the  properties  of  the  monohalog en-substituted 
acids  depend  chiefly  upon  the  relative  position  of  the  halogen  atom 
and  the  carboxyl-group. 

On  boiling  with  alkalis,  the  a-halogen-substituted  acids  are 
readily  converted  into  the  a-hydroxy-acids  by  exchange  of  halogen 
for  hydro xyl: 

CH2CI-COOH  +  KOH  =  KC1+CH2OH.COOK. 

Monochloroacetic  acid  Potassium  glycollate 

On  similar  treatment,  the  /?-halogen-substituted  acids  lose 
hydrogen  halide,  with  formation  of  unsaturated  acids: 

CH3  -  CHC1  •  CH2  •  COOH  =  CH3  •  CH :  CH .  COOH  +  HC1. 

/?-Chlorobutyric  acid  Crotonic  acid 

The  behaviour  of  the'  ^-halogen-substituted  acids  with  sodium 
carbonate  is  very  characteristic.  When  they  are  warmed  with 
its  aqueous  solution,  hydrogen  halide  and  CO2  are  simultaneously 
eliminated  from  the  molecule,  with  formation  of  an  unsaturated 
hydrocarbon : 

/CH, 

CH3.CH.CH|C02!Na|  =  CH3-CH:CH.CH3+ 

j I  pseudoButylene 

[Br 


§§  177, 178]  HALOGEN-SUBSTITUTED  ACIDS.  221 

On  boiling  with  water  or  with  an  alkali-metal  carbonate,  the 
7-halogen-substituted  acids  readily  lose  HX,  forming  lactones 
(180  and  185-186) : 

CH3-CH.CH2.CH2.CO-^CH3-CH.CH2-CH2.CO 

"Hl'O  -O 

Valerolactone 

Chloroacetic  Acids. 

177.  Monochloroacetic  acid,  CH2C1'COOH,  is  obtained  by  the 
action  of  chlorine  upon  acetic  acid,  in  presence  of  sulphur  as  a 
chlorine-carrier.     It  is  a  crystalline  solid,  melting  at  63°.     Di- 
Moroacetic    acid,    CHC12«COOH,  a  liquid  boiling  at   191°,  and 
trichloroacetic  acid,  CCls-COOH,  a  solid  melting  at  57°  and  boiling 
at  195°,  are  best  prepared  from  chloral   (201).     Trichloroacetic 
acid  is  unstable,  and  on  boiling  with  water  decomposes  into  carbon 
dioxide  and  chloroform : 

CC13-[CO^H  =  CC13H  +  CO2. 

This  is  another  example  of  the  fact  that  "  loading  "  a  carbon  atom 
with  negative  elements  and  groups  renders  the  molecule  unstable. 

Acids  with  more  than  one  Halogen  Atom  in  the  Molecule. 

178.  Isomerism  in  this  type  of  compounds  may  be  occasioned 
by  a  difference  in  position  of  the  halogen  atoms  in  the  molecule. 
Addition  of  halogen  to  an  unsaturated  acid  produces  a  compound 
with  the  halogen  atoms  linked  to  adjoining  carbon  atoms. 

The  elimination  of  hydrogen  halide  from  acids  of  this  class  affords 
a  striking  example  of  the  value  of  stereochemistry  in  explaining 
phenomena  for  which  the  ordinary  constitutional  formulae  are  unable 
to  account.  Among  them  is  the  fact  that  in  the  series  of  unsaturated 
acids  the  dibromide  of  one  modification  loses  2HBr  very  readily, 
yielding  an  acid  with  a  triple  bond,  while  the  dibromide  of  the  other 
modification  either  does  not  react  thus,  or  only  with  difficulty.  An 
example  of  this  is  afforded  by  erucic  and  brassidic  acids,  which  have 
been  proved,  by  the  method  indicated  in  140,  to  have  the  constitution 

C8H17-CH:CH-C,iHM-COOH. 

When  heated  with  alcoholic  potash  at  150°-170°,  dibromoerucic  acid, 
obtained  by  addition  of  bromine  to  erucic  acid,  readily  loses  2HBr, 


222 


ORGANIC   CHEMISTRY. 


15178 


yielding  behenolic  acid,  C8H17»Ci=C'CiiH22-COOH;  whereas  one 
molecule  of  hydrobromic  acid  is  eliminated  from  dibromobrassidic 
acid,  with  production  of  a  monobromoerucic  acid.  This  difference  is 
accounted  for  by  assigning  the  Zrans-formula  to  erucic  acid  and  the 
cis-formula  to  brassidic  acid,  as  indicated  in  Figs.  47  to  52. 


C8H17 


CUH22-C02H 


FIG.  47. — ERUCIC  ACID. 
Trans-formula. 


C8H17 


Rotated 


CUH22-C02H 


FIG.  48. — DIBROMOERUCIC 
ACID. 


FIG.  49. — DIBROMOERUCIC 

ACID. 

Each  H-atom  in  corresponding 
position  to  a  Br-atom. 


In  the  formula  for  dibromoerucic  acid,  the  tetrahedra  may  be 
rotated  so  as  to  bring  each  Br-atom  above  a  H-atom  (170),  making 
the  elimination  of  2HBr  possible  (Figs.  48  and  49):  in  that  for 
dibromobrassidic  acid,  only  one  Br-atom  and  one  H-atom  can  be 
brought  into  the  "  corresponding  positions  "  to  one  another  (Figs. 
51  and  52). 


§179] 


MONOBASIC  HYDROXY-ACIDS 
C8H17 


223 


-f-  Br2   = 


3CUH22-C02H 


FIG.  50. — BRASSIDIC  ACID. 
Cis-  formula. 

C8H17 


Rotated 


CUH22C02H 


H 


FlG.    51. DlBROMOBRASSIDIC    AdD.         FlG.    52. DlBROMOBRASSIDIC    AdD. 

Only  one  H-atom  in  corresponding 
position  to  one  Br-atom. 

II.  MONOBASIC  HYDROXY-ACIDS. 

179.  The  hydroxy-acids  are  substances  with  one  or  more 
hydroxyl-groups  and  carboxyl-groups  in  the  molecule.  The  general 
methods  for  their  formation  depend  upon  the  introduction  of 
hydroxyl-groups  and  carboxyl-groups.  They  are  produced  in  the 
following  reactions. 

1.  By  the  careful  oxidation  of  polyhydric  alcohols: 

CH3  -  CHOH  •  CH2OH  -> CH3 .  CHOH  •  COOH. 

Propyleneglycol  Lactic  acid 

2.  By  replacement  of  the  halogen  in  halogen-substituted  acids 
by  hydroxyl,  as  already  described  (150). 


224  ORGANIC  CHEMISTRY.  [§  180* 

3.  By  reduction  of  the  aldehydic  acids  and  ketonic  acids,  which 
contain  both  a  carboxyl-group  and  a  carbon  yl-group: 

CH3.CO-COOH+2H  =  CH3-CHOH.COOH. 

Pyroracemic  acid  Lactic  acid 

4.  By  the  action  of  nitrous  acid  upon  acids  with  an  amino-group 
in  the  alkyl-residue: 

NH2.CH2.COOH+HNO2  =  CH2OH.COOH  +  N2  +  H2O. 

Glycine  Glycollic  acid 

5.  By  addition  of  hydrocyanic  acid  to  aldehydes  or  ketones, 
and  hydrolysis  of  the  nitrile  thus  obtained  (101.  3),  a  method  yield- 
ing only  a-hydroxy-acids: 

/H 

CnH2n+i-CHO+HCN  =  CnH2n+i-C^-CN; 

Aldehyde  \OH 

Cyanohydriu 

/H  /H 

CnH2n+i-C;-CN+2H20  =  CnH2n+1.cAX)OH+NH3. 
\OH  V)H 

Cyanohydrin  a-Hydroxy-acid 

By  exchange  of  Br  for  OH,  acids  brominated  by  the  method  de- 
scribed in  175  yield  hydroxy-acids  identical  with  those  obtained 
by  this  cijanohydrin-synthesis.  It  follows  that  in  these  acids  the 
bromine  is  in  union  with  the  a-carbon  atom. 

6.  Oxidation  with  potassium  permanganate  effects  the  direct 
replacement  of  hydrogen  by  hydroxyl  in  acids  with  a  hydrogen 
atom  linked  to  a  tertiary  carbon  atom: 


I'soButyric  acid  a-Hydroxyisobutyric  acid 

Properties. 

1  80.  Different  compounds  are  obtained  from  the  hydroxy-acids 
by  substitution  in  the  hydroxyl-group  and  carboxyl-group  respect- 
ively. When  the  H-atom  of  the  hydroxyl-group  is  replaced  by 
alkyl,  an  acid  ether  is  obtained  : 

CHoOH  •  COOH  -»  CH2OC3H6  •  COOH. 

Glycollic  acid  Ethylgly  collie  acid 


180] 


MONOBASIC  HYDROXY-ACIDS. 


225 


Like  an  ordinary  ether,  CnH2n+1 .0-CmH2m+i,  ethylglycollic  acid 
cannot  be  saponified.  When,  on  the  other  hand,  the  H-atom  of 
the  carboxyl-group  is  exchanged  for  alkyl,  an  ester  is  produced: 

CH2OH  -  COOH  ->  CH2OH  -  COOC2H5. 

Ethyl  glycollate 

Like  other  esters,  these  compounds  can  be  saponified. 

The  introduction  of  hydroxyl  strengthens  the  fatty  acids  to  an 
extent  dependent  on  its  position  relative  to  the  carboxyl-group,  an 
effect  analogous  to  that  produced  by  the  halogens  (176).  This  is 
indicated  by  the  table,  which  contains  the  values  of  the  dissociation- 
•constant,  Wk,  for  several  acids. 


Name. 

Formula. 

104*;. 

Acetic  acid  

CH3.COOH 

0-180 

Glycollic  acid  (  Hydro  xy  acetic  acid)  
Propionic  acid  

CH.OH.COOH 
CH3.CH2.COOH 

1-52 
0-134 

Lactic  acid  (a-Hydroxypropionic  acid)  .  . 
a5-Hydroxypropionic  acid 

CH3.CHOH.COOH 
CH2OH  •  CH2  -  COOH 

1-38 
0.^1  1 

On  heating,  the  a-hydroxy-acids  readily  lose  water,  two  mole- 
cules being  simultaneously  eliminated  from  two  molecules  of  acid: 
this  reaction  takes  place  between  the  hydroxyl-group  of  one  mole- 
cule and  the  carboxyl-group  of  the  other.  Lactic  acid  yields  lactide: 


COOlHUOl— CH.CH3 


=  2H2O  + 


CH3.CH.OOC 

I  | 

COO  —  CH.CH3. 

Lactide 


The  formula  of  this  compound  indicates  that  it  is  a  double  ester,  its 
constitution  being  proved  by  its  behaviour  when  boiled  with  water 
or  dilute  acids:  like  the  esters,  it  is  saponified,  yielding  lactic  acid. 
[3-Hydroxy-acids  readily  give  up  water,  with ,  formation  of  un- 
saturated  acids: 


CH3.CH.CH.COOH 


#-Hydroxybutyric  acid 


H2O  4-CH3  •  CH :  CH  -  COOH. 

Crotonic  acid 


226  ORGANIC  CHEMISTRY.  [§§181,182 

When  a  /?-hydroxy-acid  is  boiled  with  excess  of  a  10  per  cent, 
solution  of  caustic  soda,  it  is  partly  converted  into  an  a/?-unsaturated 
acid,  and  partly  into  a  /?^-unsaturated  acid,  while  a  portion  remains 
unchanged.  An  equilibrium  is  thus  reached: 

R.CH:CH.CH2.COOH  +=>  R.CH2.CHOH.CH2.COOH  +± 
^R.CH2.CH:CH.COOH. 

If  this  reaction  is  reversible,  the  same  equilibrium  should  be  attained 
by  starting  from  the  hydroxy-acid,  or  from  either  of  the  two  unsat- 
urated  acids.  FITTIG  proved  that  this  is  actually  the  case. 

f-Hydroxy -acids  and  d-hydroxy-acids  lose  water,  with  formation 
of  inner  anhydrides,  called  lactones  (176  and  185-186) : 

CH2  •  CH2  -  CH2  •  CO  CH2 .  CH2 .  CH2 .  CO. 

I I     =H20+|  | 

pT^         H|o  o 

7-Hyclroxybutyric  acid  .  Butyrolactone 

Gly collie  Acid,  C2H4O3. 

181.  Glycollic  acid  is  present  in  unripe  grapes.  It  is  usually  pre- 
pared by  treating  monochloroacetic  acid  with  caustic  potash: 

COOH.CHjClTKlOH  =  COOH.CH2OH 


Glycollic  acid  is  a  crystalline  solid,  melting  at  80°.  It  is  very 
readily  soluble  in  water,  alcohol,  and  ether:  the  calcium  salt  dissolves 
with  difficulty  in  water.  When  distilled  in  vacua,  glycollic  acid  loses 
water,  with  formation  of  gly collide: 


CH20|H  H01CO  CH2O.CO 

I  -I       =  2H20+|  | 

COQ[H  HO|CHa  CO.Q.CH2 

Glycollide 


Hydroxypropionic  Acids, 

182.  Two  hydroxypropionic  acids  are  known,  differing  in  the 
position  occupied  by  the  hydro  xyl-group  :  they  are  a-hydroxypro- 
pionic  acid,  CH3-CHOH-COOH,  and  ^-hydroxypropionic  acid, 
CH2OH  •  CH2  •  COOH.  The  first  is  ordinary  lactic  acid. 

a  -Hydroxypropionic  acid  can  be  obtained  synthetically  by  the 
methods  described  in  179,  although  it  is  usually  prepared  by  other 


§  182]  LACTIC  ACID.  227 

means.  In  presence  of  an  organized  ferment,  called  the  "  lactic-acid 
bacillus,"  certain  sugars,  such  as  lactose,  sucrose,  and  dextrose, 
undergo  "  lactic  fermentation,"  the  principal  product  being  lactic 
acid.  These  bacilli  are  present,  for  example,  in  decaying  cheese, 
and  cannot  live  in  a  solution  of  lactic  acid  of  more  than  a  certain 
concentration:  to  make  fermentation  possible,  chalk  is  added  to 
neutralize  the  lactic  acid  formed.  Lactic  acid  can  also  be  prepared 
by  heating  dextrose  or  invert-sugar  with  caustic  soda. 

Lactic  acid  derives  its  name  from  it's  presence  in  sour  milk, 
as  a  result  of  the  fermentation  of  the  lactose  present.  The  faint 
acid  odour  possessed  by  sour  milk  is  due,  not  to  lactic  acid,  but  to 
traces  of  volatile  fatty  acids  simultaneously  formed:  lactic  acid 
itself  is  odourless.  Lactic  acid  is  also  present  in  other  fermented 
substances,  such  as  "  Sauerkraut  ";  and  in  large  quantities  in 
ensilage,  a  cattle-food  prepared  by  submitting  piles  of  grass  or 
clover  to  pressure. 

Lactic  acid  is  purified  by  distilling  the  aqueous  acid  at  very 
low  pressures  (1  mm.),  when  it  is  obtained  as  a  crystalline  solid 
melting  at  18°.  The  commercial  product  is  a  colourless,  syrupy 
liquid  of  strongly  acid  taste,  and  contains  water.  When  heated 
under  ordinary  pressure,  with  the  object  of  removing  water,  it  is 
partially  converted  into  the  anhydride  (180)  even  before  dehydra- 
tion is  complete:  this  can  be  detected  by  the  diminution  of  the 
acid-equivalent  on  titration.  Its  racemic  zinc  salt  forms  well- 
defined  crystals  with  three  molecules  of  water. 

The  constitution  of  lactic  acid  is  deduced  from  its  formation 
from  acetaldehyde  by  the  cyanohydrin-synthesis  (179,  5),  and  by 
the  oxidation  of  propyleneglycol.  When  lactic  acid  is  heated 
alone,  or  with  dilute  sulphuric  acid,  it  yields  acetaldehyde  and 
formic  acid: 


CH3-CHO|H.COOH| 


<H 


This  decomposition  may  be  regarded  as  a  reversal  of  the  cyanohydrin- 
synthesis,  and  is  characteristic  of  many  a-hydroxy-acids. 
H 

Lactic  acid,  CHa-C'COOH,    contains  one  asymmetric  carbon 
OH 


'228 


ORGANIC   CHEMISTRY. 


183 


atom.  In  accordance  with  the  principles  laid  down  in  48,  it  ought 
to  exist  in  three  isomeric  modifications,  and  all  these  are  known. 
Ordinary  lactic  acid  obtained  by  synthesis  is  racemic:  that  is, 
it  consists  of  equal  quantities  of  the  dextro-acid  and  laevo-acid, 
and  is  therefore  optically  inactive.  Dextro-lactic  acid  and  Isevo- 
lactic  acid  can  be  obtained  from  the  inactive  modification  by 
methods  described  in  195.  The  dextro-rotatory  variety  is  a 
constituent  of  meat-juices,  and  is  therefore  sometimes  called 
'"  sarcolactic  acid." 

183.  The  synthetic  lactic  acid  is  inactive,  and  hitherto  optically 
:active  products  have  not  been  prepared  from  inactive  substances 
by  wholly  chemical  means.  Since  the  inactive  modification  con- 
sists of  equal  parts  of  dextro-rotatory  and  Isevo-rotatory  substance, 
both  must  be  formed  in  equal  quantities  in  the  synthesis.  An 
explanation  of  this  phenomenon  is  afforded  by  a  consideration  of 
the  following  examples. 

The  nitrile  of  lactic  acid  is  obtained  by  the  addition  of  hydro- 
cyanic acid  to  acetaldehyde  (179,  5),  the  structural  formula  of 
which  is  represented  in  Fig.  53 : 


or 


FIG.  53. 
ACETALDEHYDE. 


FIG.  54. 
LACTONITRILE. 


H'  c 

'OH 

FIG.  55. 

LACTONITRILE. 


The  addition  of  H-CN  can  take  place  in  two  ways,  the  oxygen 
doubly  linked  to  the  central  carbon  atom  of  the  figure  becoming 
severed  either  from  the  bond  c  or  from  d.  In  the  first  case  the 
group  CN  becomes  linked  to  c  (Fig.  54),  and  a  hydroxyl-group  is 
formed  at  d:  in  the  second  case  this  is  reversed  (Fig.  55).  The 
-configurations  thus  obtained  are  mirror-images,  and  cannot  be 
made  to  coincide:  they  represent  asymmetric  C-atoms. 

The  possibility  of  the  formation  of  both  active  components  is 
thus  evident,  and  that  these  must  be  formed  in  equal  amounts  is 
made  clear  by  a  consideration  of  the  probability  of  their  formation. 
This  is  alike  for  both,  since  d  and  c  occupy  similar  positions  with 


§  184]  LACTIC  ACID.  229 

respect  to  a  and  6,  and  there  is  therefore  no  tendency  for  the  oxygen 
to  remain  linked  to  the  one  more  than  to  the  other. 

In  this  example  an  asymmetric  carbon  atom  has  resulted  from 
an  addition-reaction.  An  example  of  the  formation  by  substitution 
of  a  compound  containing  such  an  atom  is  that  of  a-bromopro- 

pionic  acid,  -R  >  ^  <  QQQJJ_>  from  Pr°Pioriic  acid>  dH>C<COOH* 


By  replacement  of  He  and  He?  respectively,  two  acids  of  opposite 
rotation  are  produced,  the  probability  of  the  formation  of  one  being 
equal  to  that  of  the  formation  of  the  other. 

Compounds  containing  an  asymmetric  carbon  atom  can  also: 
result  from  the  elimination  of  a  group,  as  in  the  formation  cf  methyl- 

ptTT  TT 

ethylacetic  acid,  p  T|  >C<rQOH'  Irom  methylethylmalonic  acid,. 


CUT  >C<COOH'  by  loss  of  C°2'     The  Probability  that  this 

d 

take  place  at  c  and  at  d  is  equal,  so  that  an  inactive  mixture  i& 
produced. 

184.  When  optically  active  lactic  acids  and  other  optically 
active  substances  are  strongly  heated,  they  are  converted  into  the 
corresponding  optically  inactive  form,  containing  equal  propor- 
tions of  the  dextro-modification  and  Isevo-modification.  This 
necessitates  the  conversion  of  one-half  of  the  optically  active  sub- 
stance into  its  optical  isomeride,  it  being  sufficient  that  two  of  the 
groups  or  atoms  linked  to  the  asymmetric  C-atom  should  change 
places.  To  convert  Fig.  56  into  its  mirror-image,  Fig.  57,  it  is  only 


FIG.  5t>.  FIG.  57. 

necessary,  for  example,  for  B  and  D  to  exchange  positions.  This  can 
only  happen  through  a  severance  of  the  bonds  between  B  and  D  and 
the  carbon  atom,  for  a  period  however  brief,  followed  by  a  reunion,, 


230  ORGANIC  CHEMISTRY.  [§  185 

either  as  at  first  B  to  b  and  D  to  rf,  or  in  the  reverse  order  D  to  b  and 
B  to  d.  The  similarity  of  the  positions  occupied  by  b  and  d  with 
respect  to  a  and  c  makes  the  probability  of  the  union  of  B  with  b 
and  D  with  d  equal  to  that  of  the  union  of  D  with  b  and  B  with  d,  so 
that  dextro-rotatory  and  Ia3vo-rotatory  molecules  are  formed  in 
equal  numbers,  and  after  heating  the  substance  is  optically  inactive. 

Optical  inactivity  is  sometimes  attained  without  the  aid  of  heat. 
WALDEN  found  that  the  dextro-rotatory  zsobutyl  bromopropionate, 
OH3.CHBr.COOC4Hy,  and  other  compounds  with  a  Br-atom  in  union 
with  an  asymmetric  C-atom,  became  optically  inactive  through  being 
kepi;  for  three  or  four  years  at  the  ordinary  temperature.  The  veloc- 
ity of  transformation  under  such  conditions,  for  most  substances  too 
small  to  be  appreciable  after  the  lapse  of  even  long  periods — and 
only  measurable  at  higher  temperatures,  which  have  an  accelerating 
effect  upon  most  reactions — has  for  these  compounds  a  measurable 
value. 

Lactones. 

185.  The  ^-hydroxy-acids  lose  water  very  readily,  with  forma- 
tion of  lactones  (176  and  180).  So  great  is  this  tendency  that 
some  ^-hydroxy-acids,  when  liberated  from  their  salts,  at  once 
give  up  one  molecule  of  water,  yielding  a  lactone.  This  phenome- 
non is  another  example  of  the  readiness  with  which  ring-com- 
pounds containing  four  carbon  atoms  are  formed  (168).  Many 
f-hydroxy-acids  are  not  known  in  the  free  state,  but  only  in  the 
form  of  esters,  salts,  or  amides.  The  lactones  are  stable  towards 
an  aqueous  solution  of  sodium  carbonate,  but  are  converted  by  the 
hydroxides  of  the  alkali-metals  into  salts  of  r-hydroxy-acids,  a 
reaction  proving  their  constitution.  They  may  be  looked  upon  as 
the  inner  esters  of  the  hydroxy-acids. 

The  lactones  can  be  prepared  by  several  methods.  Thus, 
acids  containing  a  double  bond  at  the  /^-position  or  ^-position 
(J^-acids  or  J^-acids)  are  readily  converted  into  lactones  by 
warming  with  dilute  sulphuric  acid.  This  formation  of  lactones 
may  be  regarded  as  an  addition  of  the  carboxyl-group  at  the 
double  bond: 

R.CrH:CH.CH2.CO  ->  R.CH.CH2.CH2-CO. 

II  I 

H-0  ! O 


186]  L  ACTON  ES.  231 

Unsaturated  ^r-acids  can  be  obtained  by  several  methods,  one 
being  the  action  of  aldehydes  upon  sodium  succinate  in  presence  of 
acetic  anhydride : 


H2C-COOH 

Aldehyde         Succinic  acid 


By  elimination  of  one  molecule  of  water,  there  results  a  lactonic  acid, 

CH3.CH.CH.C02H 

CH2 
O— CO 

On  dry  distillation,  this  loses  CO2,  yielding  the  unsaturated  acid: 


CH3.CH.CH.|CO2|H 

CH2  -»  CH3.CH:CH.CH2.COOH. 

O— CO 

Another  method  for  the  preparation  of  lactones  is  the  reduc- 
tion of  T'-ketonic  acids  (233,  3).  <5-Lactones  and  £ -lactones  are  also 
known. 

1 86.  On  boiling  with  water,  the  lactones  are  partly  converted 
Into  the  corresponding  hydroxy-acids,  the  quantity  of  acid  formed 
being  in  a  measure  dependent  upon  the  amount  of  water  present. 
An  equilibrium  is  attained  between  the  system  acid  and  lactone  -f 
water : 

CH2OH  -  CH2  -  CH2  •  COOH  <=>  CH2' •  CH2  -  CH2  -  CO  +  H2O. 

7-Hydroxybutyric  acid 

I O 

Butyrolactone 

If  the  molecular  concentration  per  litre  of  the  f-hydroxy- 
butyric  acid  is  A,  and  if,  after  the  lapse  of  a  time  t,  x  molecules 
have  been  converted  into  lactone,  the  velocity  of  lactone-forma- 
tion  at  that  instant,  s,  is  given  by  the  equation. 


232  ORGANIC  CHEMISTRY.  [§187 

k  being  the  reaction-constant.  But  the  reverse  also  takes  place,  the 
acid  being  regenerated  from  the  lactone  and  water.  If  the  lactone 
is  dissolved  in  a  large  excess  of  water,  no  appreciable  error  is  in- 
troduced by  assuming  the  quantity  of  the  latter  to  be  constant. 
The  velocity  s'  of  this  reverse  reaction  is  then  represented  by  the 
equation 


in  which  kf  is  again  the  reaction-constant.  The  total  velocity  of 
the  lactone-formation  for  each  instant  is,  therefore,  equal  to  the 
difference  between  these  velocities: 

dx 
s-sf^=k(A-x)-kfx  ......     (1) 

When  equilibrium  is  reached,  s  =  s';  and  if  the  value  of  x  at  this 
point  has  become  equal  to  xi,  then 

•     •     •     (2) 

Equations  1  and  2  can  be  solved  for  k  and  kf.  The  same  method 
of  calculation  may  be  applied  to  ester-formation  from  acid  and 
alcohol,  by  which  the  reaction-constant  of  the  ester-formation,  and 
of  the  ester-decomposition,  can  be  computed. 

The  lactones  form  addition-products  with  hydrobromic  acid 
as  well  as  with  water,  yielding  ^--bromo-acids,  the  constitution  of 
which  is  inferred  from  their  reconversion  into  lactone  (176).  The 
lactones  also  form  addition-products  with  ammonia,  yielding  the 
amides  of  the  ^-hydroxy-acids. 

HI.  DIBASIC  HYDROXY-ACPDS. 

187.  The  simplest  dibasic  hydroxy-acid  is  tartronic  acid, 
COOH.CHOH.COOH.  It  can  be  obtained  by  the  action  of  moist 
oxide  of  silver  upon  bromomalonic  acid,  and  is  a  crystalline  solid, 
melting  at  187°  with  evolution  of  CO2.  The  glycollic  acid, 
CHzOH.COOH,  thus  formed,  at  once  loses  water,  yielding  a  poly- 
meride  of  glycollide  (181). 

A  substance  of  greater  importance  is  malic  acid,  C4H6O5, 
which  is  present  in  various  unripe  fruits,  and  is  best  prepared  from 
unripe  mountain-ash  berries.  It  is  a  crystalline  solid,  melting  at 


§188]  MALIC  ACID  AND   TARTARIC  ACIDS.  233 

100°,  and  is  readily  soluble  in  water  and  in  alcohol.  Natural 
malic  acid  is  optically  active. 

It  is  possible  to  prove  in  several  ways  that  malic  acid  is  hydroxy- 
succinic  acid,  COOH  .CHOH.CH2- COOH.  Among  these  are  its 
reduction  to  succinic  acid  by  heating  with  hydriodic  acid,  its  con- 
version into  monochlorosuccinic  acid  by  the  action  of  phosphorus 
pentachloride,  and  so  on.  Its  alcoholic  character  is  indicated  by 
the  formation  of  an  acetate  when  its  diethyl  ester  is  treated  with 
acetyl  chloride. 

The  conversion  of  malic  acid  under  the  influence  of  heat  into 
fumaric  acid  and  malei'c  acid  has  been  already  mentioned  (169). 
In  addition  to  the  natural  Isevo-rotatory  acid,  both  a  dextro-rota- 
tory and  an  inactive  modification  are  known.  The  latter  can  be 
resolved  by  fractional  crystallization  of  its  cinchonine  salt  into  its 
two  optically  active  components.  As  indicated  by  its  structural 
formula,  malic  acid  contains  an  asymmetric  C-atom. 

Tartaric  Acids,  C4H6O6. 

1 88.  Four  acids  of  the  composition  C4H6O6  are  known,  all  with 
the  constitutional  formula 

COOH  •  CHOH  •  CHOH  -  COOH. 

They  are  called  dextro-rotatory  tartaric  acid,  loevo-rotatory  tartaric 
acid,  racemic  acid,  and  mesotartaric  acid:  the  last  two  are  optically 
inactive.  Their  constitution  is  proved  by  their  formation  from  the 
dibromosuccinic  acids — obtained  from  fumaric  acid  or  maleiic  acid 
by  the  action  of  bromine — by  boiling  their  silver  salts  with  water, 
as  well  as  by  their  production  from  glyoxat  (198)  by  the  cyano- 
hydrin  synthesis.  The  inactive  modifications  are  produced  by 
these  reactions  (183). 

In  accordance  with  the  constitutional  formula  given  above,  the 
tartaric  acids  contain  two  asymmetric  C-atoms  in  the  molecule, 
and  it  is  necessary  to  consider  how  many  stereoisomerides  are 
theoretically  possible. 

With  a  single  asymmetric  C-atom  there  are  two  optical 
isomerides,  which  can  be  denoted  by  rt  and  ^  (I.).  Addition 
of  a  second  asymmetric  C-atom',  which  may  be  dextro-rotatory 
or  Isevo-rotatory,  produces  the  combinations  II.  of  the  subjoined 
scheme.  Increase  in  the  number  of  C-atoms  to  three  gives 


234  ORGANIC  CHEMISTRY.  [§  189 

similarly  eight  isomerides  (III.)-     It  is  evident  that  for  n  asym- 
metric C-atoms  the  number  of  possible  isomerides  is  2": 
I.  f!  Zx 


II. 


III.  rlr2r3 

In  this  scheme,  all  the  asymmetric  C-atoms  are  assumed  to  be 
dissimilar,  and  the  racemic  combinations  are  left  out  of  con- 
sideration. 

Since  tartaric  acid,  however,  contains  two  similar  asymmetric 
C-atoms,  that  is  asymmetric  C-atoms  in  union  with  similar  groups, 
Zi/2  and  I2ri  become  identical,  leaving  so  far  three  isomerides 
possible.  r}r2  and  l\L2  being  able  to  unite  to  form  a  racemic 
compound,  the  total  number  of  possible  isomerides  is  raised  to  four: 

CH(OH)(COOH)     Dextro     Dextro     IJL 

tion  of  r      and 


CH(OH)(COOH)     Dextro     L*vo       LSBVO 

The  four  tartaric  acids,  C4H6O6,  correspond  in  properties  with 
the  four  theoretically  possible  isomerides.  Dextro-tartaric  acid 
and  laevo-tartaric  acid  must  be  represented  respectively  by  1  and 
3,  since  in  these  both  C-atoms  rotate  the  plane  of  polarization  in 
the  same  direction,  and  should  therefore  reinforce  each  other's 
influence.  The  optically  inactive  mesotartaric  acid  is  represented 
by  2:  its  two  asymmetric  C-atoms  rotate  the  plane  of  polarization 
equally,  but  in  opposite  directions,  and  thus  neutralize  each  other's 
effect.  Finally,  isomeride  4  is  racemic  acid. 

An  important  difference  exists  between  the  two  optically  in- 
active isomerides,  racemic  acid  and  mesotartaric  acid.  The  former, 
obtained  by  mixing  equal  quantities  of  the  dextro-acid  and  Isevo-acid, 
can  be  resolved  into  its  components:  the  latter,  consisting  only  of 
one  kind  of  molecules,  cannot  be  resolved.  The  rotation  caused  by 
the  dextro-acid  is  equal  in  .  amount  but  opposite  in  sign  to  that 
due  to  the  Isevo-acid. 

189.  EMIL  FISCHER  has  introduced  a  simple  mode  of  writing  the 
spacial  formulae  of  optically  active  compounds,  of  which  frequent 


§189] 


TARTAR1C   ACIDS. 


235 


use  will  be  made  later.     The  representation  in  space  of  two  C-atoms 

Cabc 
in  union ,  in  a  compound  |        ,  is  shown  in  Fig.  58  (168) . 

Cabc 


'6 
FIG.  58.  FIG.  59. 

If  the  two  bonds  uniting  the  two  carbon  atoms  are  supposed  to 
lie  in  the  plane  of  the  paper,  then  the  positions  of  a  and  c  are  to 
the  back,  and  of  b  to  the  front.  If  a,  6,  and  c  are  imagined  to  be 
projected  upon  the  plane  of  the  paper,  and  a  and  c  simultaneously 
so  altered  in  position  that  they  lie  in  the  same  straight  line  at 
right  angles  to  the  vertical  axis,  and  b  lies  in  this  axis  produced, 
then  projection-figure  I.  is  obtained : 

b  a 


a 
II. 


If  Fig.  58  is  rotated  round  its  vertical  axis,  so  that  a,  for  example/  lies 
in  front  of  the  plane  of  the  paper,  Fig.  59  results,  its  projection  being  repre- 
sented by  II.  These  apparently  different  configurations  are  identical. 

For  a  chain  of  four  carbon  atoms  there  is  obtained  analogously 
the  projection -figure 


236 


ORGANIC   CHEMISTRY. 


[§190 


'This  will  be  understood  if  it  is  imagined  that  the  figures  in  168 
(Fig.  33)  are  so  placed  that  the  plane  in  which  the  carbon  bonds 
lie  is  at  right  angles  to  that  of  the  paper,  and  the  figures  in  this 
position  are  projected  in  the  manner  just  described. 

190.  The  projection-formulae  for  the  four  isomeric  tartaric 
acids  are  thus  obtained.  If  the  projection-figure  for  two  asym- 
metric C-atoms  is  divided  in  the  middle  of  the  vertical  line,  and 
the  upper  half  of  the  figure  rotated  through  180°  in  the  plane  of 
the  paper,  the  similar  grouping  of  HO,  H,  and  COOH  about  the 
.asymmetric  C-atoms  in  both  halves, 
I 


HO- 


-H    and     HO- 


COOH  COOH 

indicates  that  both  C-atoms  rotate  the  plane  of  polarization  in  the 
same  direction.  We  shall  arbitrarily  assume  that  this  grouping 
occasions  dextro-rotation. 

When  the  two  carbon  atoms  are  again  united  by  transposing 
one  of  the  halves  in  the  plane  of  the  paper,  the  figure 

COOH 


H- 
HO- 


-OH 
-H 


COOH 

/results,  and  is  therefore  the  projection-formula  for  the  dextro- 
rotatory acid. 

The  grouping  with  respect  to  the  two  C-atoms  in  the  laevo- 
rotatory  acid  must  be  the  mirror-image  of  that  in  the  dextro- 
.rotatory  (48) :  thus, 


H- 


-OH     and     H- 


COOH 


-OH. 


COOH 


§  190]  TARTARIC  ACIDS.  237 

The  combination  of  these  two  gives  the  projection-formula 

COOH 


HO- 
H- 


-OH 


COOH 

for  the  Isevo-rotatory  acid. 

These  representations  of  the  constitutions  of  dextro-tartaric 
acid  and  laevo-tartaric  acid  cannot  be  made  to  coincide  by  altering 
their  position  in  the  plane  of  the  paper,*  and  are  therefore  different. 

When  the  acid  contains  a  dextro-rotatory  and  a  laBvo-rotatory 
C-atom,  as  in  mesotartaric  acid,  the  arrangement  of  the  groups 
will  be 


Dextro 


Lsevo 


-OH, 


COOH 
and  their  projection-formula 

HO- 
HO- 


COOH 


COOH 
-H 

< 

— H 


COOH 


*  These  projection-formulae  can  be  made  to  coincide  by  rotating  one  of 
them  through  180°  about  the  line  HO — H.  It  will  be  seen  from  a  model, 
however,  that  the  spatial  formulae  cannot  be  made  to  coincide  by  this  treat- 
ment. To  determine  by  means  of  projection-formu.se  whether  this  is  possible 
for  spacial  formulae,  it  is  only  admissible  to  transpose  them  in  the  plane  of 
.the  paper. 


238  ORGANIC  CHEMISTRY.  §191] 

The  projection-formula  for  racemic  acid  is 


Dextro  Lsevo 

COOH  COOH 


H- 
HO 


-OH      HO 


-H         H- 


-H 


-OH 


COOH  COOH 

Dextro-tartaric  Acid. 

191.  Potassium  hydrogen  d-tartrate,  C4H506K,  is  present  in  the 
juice  of  grapes,  and  during  alcoholic  fermentation  is  deposited  on 
the  bottom  of  the  casks,  being  even  more  sparingly  soluble  in  dilute 
alcohol  than  in  water.  The  crude  product  is  called  "argol  ";  when 
purified,  it  is  known  as  "  cream  of  tartar."  To  obtain  dextrc- 
tartaric  acid,  the  crude  argol  is  boiled  with  hydrochloric  acid,  and 
the  acid  precipitated  as  calcium  tartrate,  CaC4H4Og,  with  milk  of 
lime.  After  washing,  the  calcium  salt  is  treated  with  an  equivalent 
quantity  of  sulphuric  acid,  which  precipitates  calcium  sulphate  and 
sets  free  the  tartaric  acid :  this  can  be  obtained  by  evaporation  in 
the  form  of  large,  transparent  crystals,  without  water  of  crystalliza- 
tion, and  having  the  composition  C4H6Og. 

Dextro-tartaric  acid  melts  at  170°,  is  very  readily  soluble  in 
water,  to  a  less  extent  in  alcohol,  and  is  insoluble  in  ether.  When 
heated  above  its  melting-point  at  atmospheric  pressure,  it  loses 
water  and  yields  various  anhydrides,  according  to  the  intensity 
and  duration  of  the  heating.  On  stronger  heating,  it  turns  brown, 
with  production  of  a  caramel-like  odour,  and  at  a  still  higher  tem- 
perature chars,  with  formation  of  pyroracemic  acid  (231)  and 
pyrotartaric  acid,  COOH.CH(CH3).CH2-COOH.  It  can  be 
converted  into  succinic  acid  by  the  action  of  certain  bacteria. 

In  addition  to  the  potassium  hydrogen  tartrate  may  be  men- 
tioned the  normal  potassium  salt,  C4H4OGK2;  which  is  readily  soluble 
in  water,  and  potassium  antimonyl  tartrate, 

2[COOK  •  CHOH  •  CHOH  -  COO  (SbO)]  -f  H2O. 

On  account  of  its  medicinal  properties,  the  latter  is  known  as  "  tar- 
tar emetic."  It  is  obtained  by  boiling  potassium  hydrogen  tartrate 
with  antimony  oxide  and  water,  and  is  readily  soluble  in  water. 


191] 


TARTARIC  ACIDS. 


239 


The  precipitation  of  hydroxides  from  metallic  salts — for  exam- 
ple, copper  hydroxide  from  copper  sulphate — is  prevented  (157) 
by  the  presence  of  tartaric  acid.  The  liquid  obtained  by  dissolving 
copper  sulphate,  tartaric  acid,  and  excess  of  potassium  hydroxide 
in  water  is  called  "  FEHLING'S  solution."  It  is  an  important  means 
of  testing  the  reducing  power  of  compounds,  since  reducing  agents 
precipitate  yellowish-red  cuprous  oxide,  or  its  hydroxide,  from  the 
dark-blue  solution.  In  this  alkaline  copper  solution  the  hydroxyl- 
groups  of  the  central  C-atoms  have  reacted  with  the  copper 
hydroxide,  since  one  gramme-molecule  of  normal  alkali  tartrate  can 
dissolve  one  gramme-molecule  of  copper  hydroxide.  These  copper 
alkali  tartrates  have  also  been  obtained  in  a  crystalline  form:  thus, 
the  compound  C4H2O6Na2Cu+2H2O  is  known,  and  must  have  the 
constitutional  formula 

O-CH.COONa 
Cu<       .  +2H2O. 

O.CH.COONa 

Experiment  has  proved  that  in  aqueous  solution  this  compound 

O-CH-COO' 
is  ionized  to  JMa*  and  the  complex  amon  Cu<  .     First. 

O-CH-COO' 

the  reactions  of  the  solution  are  no  longer  those  of  copper  ions: 
although  the  liquid  is  alkaline,  copper  hydroxide  is  not  precipitated. 
Second,  on  electrolysis  the  copper  goes  towards  the  anode.  This  has 
been  studied  by  KUSTER  by  the  aid  of  the  apparatus  shown  in  Fig. 
60.  One  U-tube  contains  copper-sulphate  solution  at  6;  the  other, 


FIG.  60. — ELECTROLYSIS  OF  AN  ALKALINE  COPPER  SOLUTION. 

FEHLING'S  solution  at  d:  into  both  limbs  of  each  is  then  carefully 
poured  a  solution  of  sodium  sulphate,  a  and  c.  The  common  sur- 
faces of  the  sodium-sulphate  and  copper-sulphate  solutions  in  the 
two  U-tubes  lie  in  the  same  horizontal  plane.  When  an  electric 
current  is  passed  through  the  tubes,  preferably  arranged  in  parallel, 


240  ORGANIC  CHEMISTRY.  §192] 

and  not  in  series,  a  different  effect  is  produced  on  the  level  of  the 
surfaces  of  the  copper  solutions  in  each  tube.  In  the  copper-sulphate 
solution  a  rise  takes  place  at  the  cathode,  since  the  Cu-ions  are 
cathions,  and  tend  towards  the  cathode.  The  reverse  effect  is 
observed  in  the  FEHLING'S  solution,  indicating  that  in  it  the  copper 
is  a  constituent  of  the  anion.  The  arrows  in  the  figure  show  the 
direction  in  which  the  ions  in  each  solution  tend. 

Moreover,  the  colour  of  FEHLING'S  solution  is  a  much  more  in- 
tense blue  than  that  of  a  copper-sulphate  solution  of  equivalent 
concentration,  this  being  evidence  of  the  presence  in  FEHLING'S 
solution  of  a  complex  ion  containing  copper. 

FEHLING'S  solution  decomposes  gradually,  so  that  it  is  best  pre- 
pared as  required.  OST  has  discovered  a  much  more  stable  alkaline 
copper  solution,  applicable  to  the  same  purposes  as  that  of  FEHLING. 
It  is  a  mixture  of  copper  sulphate  with  potassium  hydrogen  carbon- 
ate and  potassium  carbonate,  and  contains  a  soluble  double  carbon- 
ate of  copper  and  potassium. 

Laevo-tartaric  Acid. 

Lcevo-tartaric  acid  is  obtained  from  racemic  acid.  With  two 
exceptions,  the  properties  of  the  laevo-acid  and  its  salts  are  identical 
with  those  of  the  dextro-modification  and  its  salts.  First,  their 
rotatory  power  is  equal,  but  opposite  in  sign:  second,  the  salts 
formed  by  the  laevo-acid  with  the  optically  active  alkaloids  differ 
in  solubility  from  those  derived  from  the  dextro-acid  (195). 

Racemic  Acid. 

192.  It  is  stated  in  184  that  optically  active  substances  can  be 
converted  by  the  action  of  heat  into  optically  inactive  compounds; 
that  is,  changed  into  a  mixture  of  the  dextro-modification  and 
laevo-modification  in.  equal  proportions.  This  change  'is  often 
facilitated  by  the  presence  of  certain  substances :  thus,  dextro- 
tartaric  acid  is  readily  converted  into  racemic  acid  by  boiling  with 
excess  of  a  concentrated  solution  of  sodium  hydroxide.  Meso- 
tartaric  acid  is  simultaneously  formed  (193). 

The  optical  inactivity  is  occasioned  by  conversion  of  one-half  of 
the  dextro-acid  into  the  Isevo-modification.  If  formula  I.  represents 
the  dextro-acid,  then  formula  II.  will  correspond  with  the  laevo-acid; 
and  the  formulae  indicate  that  the  exchange  of  groups,  by  which  an 


§193] 


TARTARIC  ACIDS. 


241 


active  compound  is  converted  into  its  optical  isomeride  (184),  must 
in  this  instance  take  place  at  both  asymmetric  C-atoms,  in  order  that 
the  dextro-acid  may  yield  its  laevo-isomeride. 


COOH 


COOH 


H- 


HO 


-OH 
-H 


HO 


H- 


COOH 
I. 


-H 
-OH 


COOH 
II. 


Racemic  acid  is  not  so  soluble  in  water  as  the  two  optically 
active  acids,  and  differs  in  crystalline  form  from  them:  the  crystals 
have  the  composition  2C4H6O6+2H2O.  In  many  of  its  salts  the 
amount  of  water  of  crystallization  differs  from  that  in  the  corre- 
sponding optically  active  salts.  Racemic  acid  is  proved  to  consist 
of  two  components  by  its  synthesis  from  solutions  of  the  dextro- 
acid  and  the  Ia3vo-acid.  If  the  solutions  are  concentrated,  heat  is 
developed  on  mixing,  and  the  less  soluble  racemic  acid  crystallizes 
out.  Racemic  acid  can  also  be  resolved  into  the  two  optically 
active  modifications  (195). 

Although  racemic  acid  in  the  solid  state  differs  from  both  dextro- 
tartaric  acid  and  Isevo-tartaric  acid,  yet  in  solution,  or  as  ester  in 
the  state  of  vapour,  it  is  only  a  mixture  of  them.  The  cryoscopic 
depression  produced  by  it  corresponds  with  the  molecular  formula 
C4H6O6;  and  the  vapour-density  of  its  ester  with  single,  instead  of 
with  double,  molecules. 

The  term  "  racemic  "  is  applied  to  substances  which  consist  of 
isomerides  of  equal  and  opposite  rotatory  power  in  equimolecular 
proportions,  and  are  therefore  optically  inactive.  This  phenom- 
enon was  first  observed  by  PASTEUR  in  his  researches  on  racemic 
acid  (195). 

Mesotartaric  Acid. 

193.  Like  racemic  acid,  mesotartaric  acid  is  optically  inactive 
but  cannot  be  resolved  into  optically  active  components.  It  is 
formed  when  dextro-tartaric  acid  is  boiled  for  several  hours  under 
a  reflux-condenser  with  a  large  excess  of  sodium  hydroxide  (192) . 


242 


ORGANIC  CHEMISTRY. 


[§193 


If  formula  I.  is  assigned  to  dextro-tartaric  acid,  it  is  evident  that 
to  convert  it  into  mesotartaric  acid,  formula  II.,  it  is  only  necessary 


( 

X)OH                                        ( 

OTT                       HO 

X)OH 

HO 

H"HO 

( 

X)OH                                       ( 

X)OH 

I.                                                              II. 

for  two  groups  in  union  with  a  single  asymmetric  C-atom  to  change 
places,  while  racemic  acid  can  only  result  through  exchange  of  the 

CO-OH 


2OH 


CO-OH 


FIG.  61. — MALEIC  ACID 
CO-OH     H 


or 


CO-OH 
H  OH 

FIG.  62. — MESOTARTARIC  ACID.     FIG.  63. — MESOTARTARIC  ACID. 

groups  linked  to  both  C-atoms.     This  affords  an  explanation  of  the 
fact  that  when  dextro-tartaric  acid  is  heated  with  dilute  hydrochloric 


1194] 


TARTARIC  ACIDS. 


243 


acid,  or  boiled  with  dilute  sodium  hydroxide,  mesotartaric  acid  is 
first  formed,  and  racemic  acid  only  after  prolonged  heating. 

Potassium  hydrogen  mesotartrate  is  readily  soluble  in  cold  water, 
differing  in  this  respect  from  the  corresponding  salts  of  the  other 
tartaric  acids. 

194.  This  view  of  the  structure  of  the  tartaric  acids  is  in  complete 
accord  with  their  relation  to  fumaric  acid  and  maleic  acid  (169),  which, 
on  treatment  with  a  dilute  aqueous  solution  of  potassium  perman- 
ganate, yield  respectively  racemic  acid  and  mesotartaric  acid  by  addi- 


HOOC 


4-»(OH), 


FIG.  64. — FUMARIC  ACID. 


_  ^_  CO-OH 

H^  OH 

FIG.  65. — RACEMIC  ACID. 

tion  of  two  hydroxyl-groups.  Addition  of  2OH  to  maleic  acid  may 
result  from  the  severance  of  the  bond  1:1'  or  2:2'  in  Fig.  61,  with 
production  of  the  configurations  represented  in  Figs.  62  and  63. 
The  projection-formulae  corresponding  with  Figs.  62  and  63  are 


244 


ORGANIC  CHEMISTRY. 
H  OH 


[§194 


HO 


HO- 


--  COOH 


and 
-COOH  H— 


H 
I. 


-COOH 


OH 
II. 


These  apparently  different  configurations  are  identical,  as  becomes 
evident  on  rearranging  I.  (p.  235)  : 


OH 


COOH- 
COOH- 


-H 
-H 


OH 

If  the  last  projection-formula  is  rotated  in  the  plane  of  the  paper 
through  180°,  it  will  coincide  with  II.  A  comparison  of  this  scheme 
with  that  in  193  shows  it  to  be  the  configuration  representing  meso- 
tartaric  acid.  It  follows  that  addition  of  two  hydroxyl-groups  to 
malei'c  acid  produces  only  mesotartaric  acid. 

A  different  result  is  obtained  by  addition  of  two  OH-groups  to 
fumaric  acid,  as  is  indicated  by  Figs.  64  and  65. 

Severance  of  the  bonds  1:1'  or  2:2'  by  addition  yields  two  con- 
figurations which  cannot  be  made  to  coincide  by  rotation.  This  ia 
made  clearer  by  the  projection-formulae 


COOH 


COOH 


HO- 


HO- 


-H 
-COOH 


HO- 


H- 


H 
OH 


-H 


-OH 


COOH 
COOH 


COOH- 
H- 


-H 
-COOH 


H- 
HO- 


OH 


-OH 
-H 


COOH 


§  195]  RESOLUTION  OF  RACEMIC  SUBSTANCES.  245 

These  projection-formulae  are  identical  with  the  configurations  repre- 
senting dextro-tartaric  and  Isevo-tartaric  acid  (p.  238). 

Hacemic  Substances,  and  their  Resolution  into  Optically  Active 

Constituents. 

J95-  Optically  active  isomerides  display  no  difference  in  their 
physical  or  in  their  chemical  properties,  except  the  rotation  of  the 
plane  of  polarized  light  in  opposite  directions,  and  certain  physio- 
logical effects  not  yet  explained.  They  have,  therefore,  the  same 
solubility,  boiling-point,  and  melting-point;  their  salts  crystallize 
with  the  same  number  of  molecules  of  water  of  crystallization;  and 
so  on.  It  follows  that  the  resolution  of  an  optically  inactive 
substance  into  its  optically  active  components  cannot  be  effected 
by  the  ordinary  methods,  since  these  are  based  on  differences  in 
physical  properties. 

PASTEUR  has  devised  three  methods  for  effecting  this  resolution. 
The  first  depends  upon  the  fact  that  racemates  sometimes  crystal- 
lize from  solution  in  two  forms,  one  corresponding  to  the  dextro- 
salt,  and  the  other  to  the  laevo-salt:  these  can  be  mechanically  sep- 
arated. PASTEUR  effected  this  for  sodium  ammonium  racemate, 
'C8H8O12Na2(NH4)2,2H2O.  Crystals  of  the  dextro-tartrate  and 
Isevo-tartrate  are  only  obtained  from  this  solution  at  temperatures 
below  28°,  the  transition-point  for  these  salts  ("  Inorganic 
Chemistry/'  70) : 

2Na(NH4)C4H4O6 •  4H2O  <=*  C8H8Oi 2Na2 (NH4)2 . 2H2O  +6H2O. 

Dextro-  +  lasvo-  Na-NH4-tartrate  Na-NH4-racemate 

Fig.  66  represents  the  crystal-forms  of  the  two  tartrates,  the 
difference  between  them  being  due  to  the  positions  of  the  planes 
a  and  b.  The  crystal-forms  are  mirror-images,  and  cannot  be 
made  to  coincide. 

Sometimes  separation  can  be  effected  by  inoculating  a  super- 
saturated solution  of  the  racemic  compound  with  a  crystal  of  another 
substance  isomorphous  with  only  one  of  the  components.  By  thus 
inoculating  a  supersaturated  solution  of  sodium  ammonium  racemate 
with  Z-asparagine  (243),  VON  OSTROMISSLENSKY  isolated  sodium 
.ammonium  dextro-tartrate  in  crystalline  form. 


246 


ORGANIC    CHEMISTRY. 


[§195 


PASTEUR'S  second  method  of  resolution  depends  upon  a  differ- 
ence in  solubility  of  the  salts  formed  by  the  union  of  optically  active 
acids  with  optically  active  bases.  When  a  dextro-acid  or  a  laBvo- 
acid  is  united  with  an  optically  inactive  base,  as  in  the  metallic 
salts,  the  internal  structure  of  the  molecule  remains  unchanged: 
the  constitution  of  the  salt-molecules,  like  that  of  the  free  acids,  can 
be  represented  by  configurations  which  are  mirror-images.  But  it 
is  otherwise  when  the  dextro-acid  and  the  laevo-acid  are  united 
with  an  optically  active  (for  example,  a  dextro-rotatory)  base:  the 
configurations  of  the  salt-molecules  are  then  no  longer  mirror- 
images,  and  identity  of  physical  properties  must  of  necessity  cease. 

Racemic  acid  can  be  thus  resolved  by  means  of  its  cinchonine 
salt,  since  cinchonine  laevo-tartrate  is  less  soluble  than  the  dextro- 
tartrate,  and  crystallizes  out  from  solution  first.  Strychnine  can 
be  advantageously  employed  in  the  resolution  of  lactic  acid,  and 
other  similar  examples  might  be  cited. 


FIG.  66. — CRYSTAL-FORMS  OF  THE  SODIUM  AMMONIUM  TARTRATES. 

The  conversion  of  enantiomorphic  isomerides  into  derivatives 
with  configurations  which  are  no  longer  mirror-images  of  one  an- 
other can  be  otherwise  effected:  thus,  for  acids,  by  the  formation 
of  an  ester  with  an  optically  active  alcohol.  The  velocity  of  ester- 
formation  with  an  optically  inactive  alcohol  must  be  the  same  for 
both  isomerides,  on  account  of  the  perfectly  symmetrical  structure 
of  the  esters  formed;  but  with  an  optically  active  alcohol  the  two 
isomerides  are  not  esterified  at  the  same  rate,  since  the  compounds 
formed  are  no  longer  mirror-images  of  one  another.  MARCKWALD 
found  that  when  racemic  mandelic  acid  (324),  is  heated  for  one 
hour  at  155°  with  menthol  (365),  an  active  alcohol,  the  non- 
esterified  acid  is  laevo-rotatory. 

The  third  method  of  fission  devised  by  PASTEUR  depends   on 


§  196]  RESOLUTION  OF    RACEMIC   SUBSTANCES.  247 

the  action  of  mould-fungi  (Penicillium  glaucum),  or  of  bacteria. 
Thus,  when  racemic  lactic  acid  in  very  dilute  solution  is  treated 
with  the  Bacillus  acidi  Icevolactici,  after  addition  of  the  necessary 
nutriment  for  the  bacteria,  the  optically  inactive  solution  becomes 
laevo-rotatory,  since  only  the  dextro-rotatory  acid  is  converted  by 
the  bacilli  into  other  substances.  A  dilute  solution  of  racemic  acid, 
into  which  traces  of  the  mould-fungus  Penicillium  glaucum  have 
been  introduced,  becomes  laBvo-rotatory,  the  fungus  propagating 
itself  with  decomposition  of  the  dextro-rotatory  acid. 

The  second  and  third  methods  of  resolution  are  alike  in  prin- 
ciple. During  their  growth  the  bacteria  and  fungi  develop  sub- 
stances called  enzymes  (222),  which  decompose  compounds  by 
means  hitherto  unexplained.  These  enzymes  are  optically  active; 
hence,  a  difference  in  their  action  on  the  optical  isomerides,  analo- 
gous to  that  described  in  the  previous  paragraph,  is  to  be  expected. 

196.  When  a  racemic  substance  is  liquid  or  gaseous,  it  consists 
only  of  a  mixture  of  the  two  enantiomorphic  isomerides:  an  ex- 
ample of  this  is  afforded  by  racemic  acid  in  solution  and  in  the 
form  of  esters  (192).  If  the  substance  is  crystalline,  there  are  three 
possibilities. 

First,  the  individual  crystals  may  be  dextro-rotatory  or  Isevo- 
rotatory,  so  that  the  two  modifications  can  be  mechanically 
separated.  This  is  expressed  by  the  statement  that  the  racemic 
substance  is  a  conglomerate  of  the  isomerides. 

Second,  it  may  be  a  true  compound  of  the  dextro-modification 
and  Isevo-modification,  a  racemic  compound  or  racemoid,  its  forma- 
tion being  comparable  to  that  of  a  double  salt,  when  a  solution 
containing  two  salts  is  allowed  to  crystallize  under  certain  conditions. 

The  third  possibility  is  also  analogous  to  the  crystallization  of 
Bait-solutions,  whereby  crystals  are  sometimes  obtained  containing 
both  salts,  but  in  proportions  varying  in  different  crystals.  It 
sometimes  happens  that  the  salts  crystallize  together  in  all  propor- 
tions, but  usually  these  can  vary  only  between  certain  limits.  This 
simultaneous  crystallization  of  salts  yields  the  so-called  mixed  crys- 
tals; and  optical  isomerides  produce  pseudoracemic  mixed  crystals. 

The  variety  of  crystals  obtained  from  a  given  solution  or  fused 
mass  of  a  racemic  substance — a  conglomerate,  a  racemic  compound, 
or  pseudoracemic  mixed  crystals — depends  upon  the  temperature 
of  crystallization,  and  upon  other  conditions.  An  example  of  this 


248  ORGANIC  CHEMISTRY.  [§197 

is  afforded  by  sodium  ammonium  racemate  (195).  when  concen- 
trated above  28°  the  racemate  crystallizes  from  the  solution  of  this 
salt;  below  this  temperature  a  mixture  of  the  individual  tartrates 
— the  conglomerate — is  obtained. 

BAKHUIS  ROOZEBOOM  has  indicated  a  method  of  distinguishing 
between  these  three  classes  of  compounds.  For  a  conglomerate, 
this  is  simple.  A  saturated  solution  is  made:  it  must  be  optically 
inactive,  and  saturated  alike  for  the  dextro-rotatory  and  for  the 
laevo-rotatory  body.  If  now  the  solid  dextro-compound  or  Isevo- 
compound  is  added,  and  the  mixture  agitated,  nothing  more  will 
dissolve,  the  liquid  being  already  saturated  with  respect  to  the  two 
isomerides:  the  amount  of  dissolved  substance  is  still  the  same,  and 
the  solution  remains  optically  inactive.  On  the  other  hand,  if  a 
racemic  compound  was  present,  although  the  solution  was  saturated 
in  the  first  instance  with  regard  to  this,  it  is  unsaturated  with  re- 
spect to  the  two  optically  active  modifications:  addition  of  the 
solid  dextro-rotatory  or  laevo-rotatory  substance  will  cause  a  change 
in  the  total  quantity  of  solid  dissolved,  and  the  liquid  will  become 
optically  active.  Less  simple  methods  are  sometimes  necessary  to 
detect  pseudoracemic  mixed  crystals. 

IV.  POL YB ASIC   HYDROXY- ACIDS. 

197.  Of  these  acids  it  will  be  sufficient  to  describe  the  tribasic 
citric  acid,  C6H8O7,  which  is  widely  distributed  in  the  vegetable 
kingdom,  and  is  also  found  in  cows'  milk.  It  is  prepared  from  the 
juice  of  unripe  lemons,  which  contains  6-7  per  cent.  Tricalcium 
citrate  dissolves  readily  in  cold  water,  but  very  slightly  in  boiling 
water:  this  property  is  employed  in  the  separation  of  the  acid  from 
lemon-juice,  it  being  obtained  in  the  free  state  by  addition  of  sul- 
phuric acid  to  the  citrate.  Another  technical  method  for  its  prepa- 
ration depends  upon  the  fact  that  certain  mould-fungi  (Citromyces 
pfefferianus  and  C.  glaber]  produce  considerable  quantities  of  citric 
acid  from  dextrose  or  sucrose. 

Citric  acid  can  be  obtained  synthetically  by  a  method  prov- 
ing its  constitution.  On  oxidation,  symmetrical  dichlorohydrin, 
CH2C1.CHOH.CH2C1  (158),  is  transformed  into  symmetrical  di- 
chloroacetone,  CH2C1  •  CO  •  CH2C1.  The  cyanohydrin-synthesis  con- 


§197]  CITRIC   ACID.  249 

/OH 

verts  this  into  CH2C1-C—  CH2C1,  and  hydrolysis  yields  the  hydro  xy- 

\CN 
/OH 
acid,   CH2C1-C—  CH2C1.      On   treatment   of   this   compound  with 

\COOH 

potassium  cyanide,  a  dicyanide  is  formed,  which  can  be  hydro- 
lyzed  to  citric  acid: 

CH2-CN         CH2.COOH 
'OH  '      OH 

COOH   ' 


CH2-CN         CH2.COOH 

The  alcoholic  character  of  citric  acid  is  indicated  by  the  forma- 
tion of  an  acetyl-compound  from  triethyl  citrate  and  acetyl  chloride. 

Citric  acid  forms  well-defined  crystals  containing  one  molecule 
of  water  of  crystallization,  and  is  readily  soluble  in  water  and  alco- 
hol. It  loses  its  water  of  crystallization  at  130°,  and  melts  at  153°. 
It  is  employed  in  the  manufacture  of  lemonade,  and  in  calico- 
printing. 


DIALDEHYDES  AND  DIKETONES :  HALOGEN-SUBSTITUTED 
ALDEHYDES   AND   KETONES. 


Dialdehydes. 

198.  The  simplest  member  of  the  series  of  dialdehydes,  glyoxal, 
is  a  combination  of  two  aldehydo-groups,  Q^C — V\r\-  It  is  best 

prepared  by  carefully  floating  a  layer  of  water  on  the  surface  of 
strong  nitric  acid  contained  in  a  tall  glass  cylinder,  and  pouring 
ethyl  alcohol  on  the  surface  of  the  water,  care  being  taken  that 
the  layers  do  not  mix.  The  nitric  acid  and  alcohol  diffuse  into 
the  water;  and  the  alcohol  is  slowly  oxidized  to  glyoxal,  glycollic 
acid,  oxalic  acid,  and  other  substances. 

Thus  prepared,  glyoxal  is  a  colourless,  amorphous  substance: 
when  moist,  it  dissolves  readily  in  water,  but  very  slowly  after 
complete  drying  in  vacuo  at  110°-120°.  It  is  a  polymeride  of  un- 
known molecular  weight ,  although  its  aqueous  solution  reacts  as 
though  it  contained  only  simple  molecules.  Distillation  of  this 
polymeride  with  phosphoric  anhydride  evolves  an  emerald-coloured 
gas,  condensable  by  cooling  to  beautiful  yellow  crystals,  which  at 
a  lower  temperature  become  colourless.  They  melt  at  15°,  and 
the  yellow  liquid  thus  obtained  boils  at  51°.  It  is  unimolecular 
glyoxal,  and  can  only  exist  as  such  for  a  short  time:  traces  of  water 
readily  polymerize  it.  The  unimolecular  form  is  the  simplest  type 
of  coloured  compound,  containing  only  carbon,  hydrogen,  and 
oxygen. 

The  combination  of  glyoxal  with  two  molecules  of  sodium 
hydrogen  sulphite,  and  the  formation  of  a  dioxime,  prove 
it  to  be  a  double  aldehyde.  It  also  has  the  other  properties  pecul- 
iar to  aldehydes,  such  as  the  reduction  of  an  ammoniacal  silver 
solution  with  formation  of  a  mirror.  On  oxidation,  it  takes  up 
two  atoms  of  oxygen,  yielding  oxalic  acid,  of  which  it  is  the  dial- 

250 


§  199]  DIKETONE&.  251 

dehyde.  Treatment  with  caustic  potash  converts  glyoxal  into 
glycollic  acid,  one  aldehydo-group  being  reduced  and  the  other 
oxidized.  This  reaction  may  be  explained  by  the  assumption 
that  an  addition-product  with  water  is  formed,  in  accordance  with 
the  scheme 

C^.C^  +  H2O  =  CH2OH.COOH. 

Glycollic  acid 

TT  TT 

Succindialdehyde,    QC-CH2-CH2-CQ,   has   been  prepared    by 

HARRIES  by  the  action  of  ozone  upon  a  chloroform  solution  of 
diallyl,  CH2:CH-CH2— CH2-CH:CH2.  An  addition-product— a 
diozonide — is  formed, 

CH2  •  CH  •  CH2 — CH2  •  CH  •  CH2, 

\/  \/ 

03  03 

each  double  linking  uniting  with  one  molecule  of  ozone.  This 
diozonide  is  a  syrup-like,  explosive  liquid.  When  heated  slowly 
with  water,  it  decomposes,  forming  succindialdehyde. 

HARRIES  has  prepared  several  analogous  ozonides,  each  double 
linking  always  taking  up  O3.  Water  decomposes  these  ozonides  in 
accordance  with  the  scheme 


+  H2O  =  >CO+OC<+H2O2. 

03 

The  formation  cf  these  ozonides  and  their  decomposition  by 
water  afford  an  excellent  method  for  determining  the  position  in 
the  molecule  of  double  linkings.  Its  application  to  the  case  of 
olei'c  acid  has  confirmed  the  formula  indicated  in  137. 

Diketones. 

199.  Thediketones  contain  two  carbonyl-groups:  their  proper- 
ties and  the  methods  employed  in  their  preparation  depend  upon 
the  relative  position  of  these  groups.  1 : 2-Diketones  with  the 

12  123 

group  —CO  •  CO—  are  known :  1 : 3-diketones  with  —CO  •  CH2  •  CO—: 

1234 

l:4-diketones  with  —  CO-CH2.CH2.CO— :  and  so  on. 

1 :2-Diketones  cannot  be  obtained  by  the  elimination  of  chlorine 


252  ORGANIC  CHEMISTRY.  [§  200' 

from  the  acid  chlorides  by  the  action  of  a  metal,  in  accordance  with 
the  scheme 


R-CO|Cl+Na2+CT]OC*R. 

Their  preparation  is  effected  by  the  action  of  amyl  nitrite  and  a 
small  proportion  of  hydrochloric  acid  on  a  ketone,  one  of  the  CH2- 
groups  being  converted  into  C=NOH: 


R-CO-C 


R-CO.C.R 


NOH  NOH 


These  compounds  are  called  isonitrosoketones.  When  boiled  with 
dilute  sulphuric  acid,  the  oxime-group  is  eliminated  as  hydroxyl- 
amine,  with  formation  of  the  diketone.  The  ketoaldehydes  are  both 

TT 

ketones  and  aldehydes,  and  contain  the  group  — CO»C\     :   they, 


too,  can  be  obtained  by  this  method. 

Diacetyl,  CH3-CO»CO-CH3,  can  be  prepared  from  methylethyl- 
ketone  in  the  manner  indicated.  It  is  a  yellow  liquid  of  pungent, 
sweetish  odour,  and  is  soluble  in  water:  its  vapour  has  the  same 
colour  as  chlorine.  Diacetyl  boils  at  88°,  and  has  a  specific  gravity 
of  0*973  at  20°.  Its  behaviour  points  to  the  presence  of  two  car- 
bony  1-^roups  in  the  molecule:  thus,  it  adds  on  2HCN,  yields  a 
mono-oxime  and  a  dioxime,  and  so  on.  The  adjacency  of  the 
two  carbonyl-groups  in  diacetyl  is  proved  by  its  quantitative  con- 
version into  acetic  acid  under  the  influence  of  hydrogen  peroxide: 


CH3.CO— 

+  OH 


CO-CH3  _>2CH3.CO.OH. 


OH 


200.  1'3-Diketones  can  be  prepared  by  a  condensation-methotl 
of  general  application  discovered  by  CLAISEN  and  WISLICENUS. 
Sodium  ethoxide  is  the  condensing  agent.  An  addition-product 
is  formed  by  the  interaction  of  this  substance  and  an  ester: 

*Q  Na  yONa 

R'C\nr  TT  +or  TT  =R'^OC2H5. 
\OC2H5      )C2H5  \OC2H5 

The  addition-product  is  then  brought  into  contact  with  a  ketone 
R'-CO-CH3,  two  molecules  of  alcohol  being  eliminated  wHh  forma- 
tion of  a  condensation-product: 


200]  D1KETONES.  253- 

,ONa 


R.OHOC2H6     H 
I*+H 


xONa 
CH  •  CO  •  R'  =  R  -  C<  +2C2H5OH. 


On  treatment  of  this  compound  with  a  dilute  acid,  the  sodium 
atom  is  replaced  by  hydrogen.  This  might  produce  a  compound 
with  a  hydro  xyl-group  attached  to  a  doubly-linked  carbon  atom; 
but  usually  compounds  of  this  type  are  unstable,  the  group- 
OH 

—  C=CH  —  changing  to  —  CO  —  CH2  —  .     The  principle  applies  in 

OH 

the  present   instance,         •  yielding  a   l:3-diketone, 

H  •  C=:CH  •  CO  •  K, 

R.CO—  CH2—  CO-R'. 

CLAISEN  has  found  that  sodamide,  Na-NH2,  can  be  substituted 
advantageously  for  sodium  ethoxide  in  the  condensation  of  ketones- 
with  esters.  Frequently,  it  not  only  facilitates  the  reaction,  but 
increases  the  yield. 

Another  method  for  the  preparation  of  1  :  3-diketones  is  the  action. 
of  acid  chlorides  on  the  sodium  compounds  of  acetylene  homologues: 


Sodio-n-amylacetylene        Acetyl  chloride 

By  treating  this  ketone  with  concentrated  sulphuric  acid,  water  is 
added,  and  the  desired  diketone  obtained: 


0    H2 

These  diketones  have  a  weak  acidic  character,  their  dissocia- 
tion-constants being  very  small.  Among  others,  that  of  acetyl- 
acetone,  CH3-CO'CH2'CO'CH3,  has  been  determined.  They  con- 
tain two  H-atoms  replaceable  by  metals.  These  must  belong  to 
the  methylene-group  between  two  negative  carbonyl-groups;  for  if 
the  other  hydrogen  atoms  could  be  thus  exchanged  for  metals, 
there  is  no  reason,  since  they  are  of  equal  value,  that  two,  and  only 
two,  should  be  replaceable. 

Acetylacetone  is  obtained  by  the  condensation  of  ethyl  acetate  and. 
acetone.  It  is  a  colourless  liquid  of  agreeable  odour,  boils  at  137°, 
and  has  a  specific  gravity  of  0-979  at  15°.  When  boiled  with  water, 
it  decomposes  into  acetone  and  acetic  acid,  a  reaction  affording 


254  ORGANIC   CHEMISTRY.  [§  201 

another  example  of  the  instability  of  compounds  containing  a  car. 
bon  atom  loaded  with  negative  groups. 

Among  the  salts  of  acetylacetone  is  the  copper  salt,  (C5H7O2)2Cu, 
which  is  sparingly  soluble  in  water;  and  the  volatile  aluminium  salt, 
(C5H7O2)3A1.  By  a  determination  of  the  vapour-density  of  this 
compound,  COMBES  has  shown  that  the  aluminium  atom  is  tervalent. 

These  metallic  compounds  have  properties  differing  from  those 
of  ordinary  salts.  Unlike  true  salts,  they  are  soluble  in  benzene, 
chloroform,  and  other  organic  solvents.  Their  aqueous  solutions  are 
almost  non-conductors  of  electricity.  They  either  do  not  answer  to 
the  ordinary  tests  for  the  metals,  or  else  react  very  slowly.  The 
ferric  and  aluminium  salts,  in  which  both  base  and  acid  are  very 
weak,  do  not  undergo  hydrolytic  dissociation,  but  diffuse  unchanged 
through  parchment-paper.  In  these  respects  they  resemble  mercuric 
cyanide  ("Inorganic  Chemistry,"  274),  which  is  practically  not 
ionized  in  aqueous  solution,  and  therefore  lacks  all  the  properties 
characteristic  of  ordinary  salts. 

A  type  of  the  1 : 4-diketones  is  acetonylacetone, 
CH3  •  CO  •  CH2  -  CH2  •  CO  -  CH3; 

the  preparation  of  which  is  described  in  233,  4.  It  is  a  colour- 
less liquid  of  agreeable  odour:  it  boils  at  193°,  and  has  a  specific 
gravity  of  0-970  at  21°.  Acetonylacetone  and  other  1  ^-dike- 
tones  yield  cyclic  compounds,  which  are  dealt  with  in  392-396. 

Halogen-substituted  Aldehydes. 

>H 

201.  Chloral  or  trichloroacetaldehyde,  CC13«C^     ,  is  of  great 

therapeutic  importance,  since  with  one  molecule  of  water  it  forms 
a  crystalline  compound  known  as  chloral  hydrate,  and  employed  as  a 
soporific.  Chloral  is  technically  prepared  by  saturating  ethyl  alcohol 
with  chlorine.  The  alcohol  must  be  as  free  from  water  as  possible, 
and  the  chlorine  carefully  dried.  At  first  the  reaction-mixture  is 
artificially  cooled,  but  after  a  few  days  the  process  becomes  less 
energetic,  and  the  temperature  is  slowly  raised  to  60°,  and  finally 
to  100°. 

The  reaction  may  be  explained  by  assuming  that  the  alcohol 
is  first  converted  into  aldehyde,  which  is  then  transformed  into 
acetal,  dichloroacetal,  and  trichloroacetal:  the  last  compound  is 


§  201]  CHLORAL.  255 

converted,  by  the  hydrochloric  acid  produced,  into  chloral  alcohol- 

r\c*  TIT 

ate,   CC13-CH<QTT2    5.       Dichloroacetal    and    other   intermediate 
products  of  this  reaction  have  been  isolated: 


CH3-CH2OH'+C12  • 

Alcohol 


Aldehyde 


Acetal 


Trichloroacetal 


Dichloroacetal 

OC2H5 
OH      * 

Chloral  alcoholate 


The  final  product  of  chlorination  is  a  crystalline  mixture  of  chloral 
alcoholate,  chloral  hydrate,  and  trichloroacetal,  from  which  chloral 
is  obtained  by  treatment  with  concentrated  sulphuric  acid.  It  is 
an  oily  liquid  of  penetrating  odour,  boiling  at  97°,  and  having  a 
specific  gravity  of  1-512  at  20°.  When  treated  with  water,  it  is 
converted  with  evolution  of  heat  into  the  well-crystallized  chloral 
hydrate,  m.  p.  57°.  To  this  compound  is  assigned  the  formula 

as  it  does  not  show  all  the  aldehyde-reactions. 

For  example,  it  does  not  restore  the  red  tint  of  a  solution  of 
magenta  (374)  which  has  been  decolorized  with  sulphurous  acid 
(107,8).  Chloral  hydrate  is,  therefore,  one  of  the  few  compounds 
containing  two  OH-groups  in  union  with  a  single  C-atom  (230 
and  234)  . 

Otherwise,  chloral  behaves  as  an  aldehyde:  for  instance,  it 
reduces  an  ammoniacal  silver  solution  with  formation  of  a  mirror, 
combines  with  sodium  hydrogen  sulphite,  and  is  oxidized  by  nitric 
acid  to  trichloroacetic  acid.  Solutions  of  the  alkalis  decompose 
it  at  ordinary  temperatures  with  formation  of  chloroform  and 
formic  acid: 


CC13. 

+  H 


rH 

UO  =  CC13H  + 

HO 


^^^ 


256  ORGANIC  CHEMISTRY.  [§201 

In  dilute  solutions  of  about  centinormal  strength,  and  at  low 
temperature,  this  reaction  has  a  measurable  velocity.  Experiment 
has  proved  it  to  be  unimolecular,  and  not  bimolecular  as  indicated 
by  the  equation.  This  phenomenon  is  explicable  by  assuming 
preliminary  combination  of  the  base  and  chloral  hydrate  to  form  a 

OTT 
salt  of  the  type  CC13  *  CH  <  Q j^>     subsequently     decomposed     into 

chloroform  and  formate.  The  electric  conductivity  of  a  mixture  of 
solutions  of  chloral  hydrate  and  a  base  also  indicates  a  union  of  the 
molecules. 

On  account  of  its  purity,  chloroform  prepared  in  this  manner  is. 
preferred  for  anesthetization. 

The  formation  of  chloroform  from  chloral  by  the  action  of 
alkaline  liquids  originally  suggested  the  use  of  chloral  as  a  soporific: 
it  was  expected  that  the  alkaline  constituents  of  the  blood  would 
decompose  it  with  the  formation  of  chloroform  in  the  body  itself. 
LIEBREICH  showed  that  chloral  has  in  fact  a  soporific  action,  but 
more  recent  investigation  has  proved  this  to  be  independent  of  the 
formation  of  chloroform,  since  the  chloral  is  eliminated  from  the 
system  as  a  complicated  derivative,  urochloralic  acid. 


ALDEHYDO-ALCOHOLS  AND  KETO-ALCOHOLS  OR 
SUGARS. 


202.  Aldehyde-alcohols  and  keto-alcohols  are  natural  products, 
and  are  very  widely  distributed.  They  are  called  carbohydrates, 
sugars,  or  saccharides.  They  contain  one  carbonyl-group  and 
several  hydroxyl-groups.  One  of  the  hydroxyl-groups  must  be  linked 
directly  to  a  carbon  atom  in  union  with  the  carbonyl-group,  so  that  the 
•characteristic  group  of  these  compounds  is  — CHOH — CO — . 

The  sugars  are  classified  as  polyoses  and  monoses.  On  hydrolysis, 
the  polyoses  yield  monoses,  which  have  lower  molecular  weights 
than  their  parent  substances,  but  possess  all  the  properties  charac- 
teristic of  the  sugars.  The  monoses  do  not  admit  of  further 
hydrolysis  to  simpler  sugars.  They  will  be  considered  first. 

Nomenclature  and  General  Properties  of  the  Monoses  and  their 

Derivatives. 

When  the  monoses  are  aldehydes  they  are  called  aldoses, 
and  when  ketones,  ketoses.  The  number  of  carbon  atoms  in  the 
molecule  is  indicated  by  their  names:  thus,  pentose,  hexose,  heptose, 
etc.  To  distinguish  between  aldoses  and  ketoses  the  prefixes 
"aldo-"  and  "keto-"  respectively  are  used;  as  aldohexose,  keto- 
hexose,  and  so  on. 

When  the  polyoses  may  be  regarded  as  derived  from  two  monose 
molecules  by  the  elimination  of  one  molecule  of  water,  they  are 
called  dioses;  thus,  hexodioses  when  they  are  formed  from  two 
molecules  of  hexose.  The  polyoses  derived  from  three  monose 
molecules  by  the  elimination  of  two  molecules  of  water  are  called 

trioses;  as  hexotriose,  etc. 

257 


258  ORGANIC  CHEMISTRY.  [§203 

Like  other  aldehydes,  the  aldoses  are  converted  by  oxidation 
into  monobasic  acids  containing  the  same  number  of  carbon  atoms, 
the  pentoses  yielding  the  monobasic  pentonic  acids,  the  hexoses  the 
hexonic  acids,  etc.  The  oxidation  can  be  carried  further;  for  the 

/H 

general  formula  of  an  aldose  is  CH2OH- (CHOH)n-C<^      (204), 

and  the  group — CH2OH  can  be  oxidized  to  carboxyl,  yielding  a 
dibasic  acid  containing  the  same  number  of  carbon  atoms  as  the 
aldose  from  which  it  is  derived.  On  oxidation,  the  ketoses  yield 
acids  containing  a  smaller  number  of  carbon  atoms. 

On  reduction,  the  aldoses  and  ketoses  take  up  two  hydrogen 
atoms,  with  formation  of  the  corresponding  alcohols:  thus,  hexose 
yields  a  hexahydric  alcohol,  and  pentose  a  pentahydric  alcohol 
(204  and  207). 

203.  Four  reactions  are  known  which  are  characteristic  of  all 
monoscs:  two  of  these  they  possess  in  common  with  the  aldehydes 
(107). 

1.  They  reduce  an  ammoniacal  silver  solution  on  warming, 
forming  a  metallic  mirror. 

2.  When  warmed  with  alkalis,  they  give  a  yellow,  and  then  a 
brown,  coloration,  and  ultimately  resinify. 

3.  When  an  alkaline  copper  solution  (FEHLING  or  OST,  191) 
is  heated  with  a  solution  of  a  monose,  reduction  takes  place,  with 
formation  of  yellow-red  suboxide  of  copper. 

4.  When  a  monose  is  heated  with  excess  of  phenylhydrazine, 
CeHs-NH-NH^,  in  dilute  sulphurous-acid  solution,  a  yellow  com- 
pound, crystallizing  in  fine  needles,  is  formed:   substances  of  this 
type  are  insoluble  in  water,  and  are  called  osazones.     Their  for- 
mation may  be  explained  as  follows. 

It  is  mentioned  in  202  that  the  sugars  are  characterized  by 
containing  the  group  — CHOH — CO — .  The  action  of  phenyl- 
hydrazine  on  a  carbonyl-group  has  already  been  explained  (103) ; 
water  is  eliminated,  and  a  hydrazone  formed : 


NHC6H5  +  H20. 


A  second  molecule  of  phenylhydrazine  then  reacts  with  the  group 
— CHOH — ,  from  which  two  hydrogen  atoms  are  eliminated,  the 


§  204]  MOXOSES.  259 

molecule  of  phenylhydrazine  being  decomposed  into  ammonia  and 
aniline: 

C6H5-NH-NH2  =  C6H5-NH2  +  NH3. 

Pheuylhydrazine  Aniline 

+      H  H 

The  elimination  of  two  hydrogen  atoms  from  the  group  — CHOH — 
converts  it  into  a  carbonyl-group,  — CO — ,  with  which  a  third 
molecule  of  phenylhydrazine  reacts,  forming  a  hydrazone,  so  that 

I  I 

CHOH  C=rN.NHC6H5 

the  group    |  is  converted  into    |  .     This  group 

CO  Cr=N.NHC6H5 

I  I 

is  characteristic  of  the  osazones. 

The  osazones  dissolve  in  water  with  difficulty.  This  property 
makes  them  of  service  in  the  separation  of  the  monoses,  which  are 
very  soluble  in  water,  and  crystallize  with  great  difficulty,  especially 
in  presence  of  salts,  and  hence  often  cannot  be  purified  by  crystal- 
lization. By  means  of  the  sparingly  soluble  osazones,  however,  they 
can  be  separated:  the  osazones  are  readily  obtained  in  the  pure 
state  by  crystallization  from  a  dilute  solution  of  pyridine  (387). 
Moreover,  the  identity  of  the  monose  can  be  established  by  a  deter- 
mination of  the  melting-point  of  the  osazone  obtained  from  it. 


Constitution  of  the  Monoses. 

204.  It  is  shown  later  that  the  constitution  of  all  the  monoses 
follows  from  that  of  the  aldohexoses,  the  structure  of  which  can  be 
arrived  at  as  follows: 

1.  The  aldohexoses  have  the  molecular  formula  C6H12O6. 

2.  The  aldohexoses  are  aldehydes,  and,  therefore,  contain  a 
carbonyl-group  in  the  molecule.     This  follows  from  the  facts  that 
they  show  the  reactions  characteristic  of  aldehydes;   that  they  are 
converted  by  oxidation  into  acids  containing  the  same  number  of 
C-atoms,  and  by  reduction  into  an  alcohol;    and  that  they  form 
addition-products  with  hydrocyanic  acid. 

3.  All  known  hexoses  contain  a  normal  chain  of  six  carbon 
atoms,  since  they  can  be  reduced  to  a  hexahydric  alcohol,  which, 


260  ORGANIC  CHEMISTRY.  [§205 

on  further  reduction  at  a  high  temperature  with  hydriodic  acid, 
yields   n-secondary   hexyl   iodide,   C^-C 


The  constitution  of  this  iodide  is  inferred  from  the  fact  that  it  can 
be  converted  into  an  alcohol,  which  on  oxidation  yields 

CH3.CH2-CO-CH2.CH2.CH3; 

for  on  further  oxidation  this  is  converted  into  n-butyric  acid  and 
acetic  acid. 

4.  The  hexoses  have  five  hydroxyl-groups,  since,  when  heated 
with  acetic  anhydride  and  a  small  quantity  of  sodium  acetate  or 
zinc  chloride,  they  yield  penta-acetyl-derivatives. 

These  facts  indicate  the  existence   in  an  aldohexose  of 

a  normal  carbon  chain,  C  —  C  —  C  —  C  —  C  —  C; 

TT 

an  aldehyde-group,         C  —  C  —  C  —  C  —  C  —  C       ;  and 


C— C— C— C— C— 
five  hydroxyi-groups, 

OHOHOHOHOH 

There  are  six  other  hydrogen  atoms  in  the  formula  C6Hi2O6,  and 
these  will  fit  in  with  the  last  scheme,  if  the  C-atoms  of  the  chain 
are  singly  linked  to  each  other:  the  formula  of  an  aldohexose  will 
then  be 

TT 

CH2 — CH — CH — CH — CH — C^, 
|  |         |          |         |  \0- 

OH      OH    OH    OH    OH 

205.  In  these  formulae  a  somewhat  arbitrary  assumption  has 
been  made  as  to  the  distribution  of  the  hydroxyi-groups  and  hydro- 
gen atoms  relative  to  the  carbon  atoms;  it  is,  however,  in  accord- 
ance with  the  principle  (149)  that  a  carbon  atom  cannot  usually 
have  linked  to  it  more  than  one  hydroxyl-group.  A  more  con- 
vincing proof  of  the  fact  that  the  monoses  do  not  contain  two 
hydroxyi-groups  attached  to  the  same  carbon  atom,  is  afforded 
by  the  following  considerations. 

When  a  hexose,  CeH^Oe,  is  reduced  to  a  hexahydric  alcohol, 
only  two  hydrogen  atoms  are  added,  and  this  addition 


§205]  MONOSES.  261 

must  take  place  at  the  doubly-linked  oxygen  atom,  since  the  carbon 
chain  remains  unbroken.  If  the  hexose  contains  two  hydroxyl- 
groups  attached  to  one  carbon  atom,  so  must  also  the  hexahydric 
alcohol  derived  from  it.  Compounds  containing  a  C-atom  linked 
to  two  OH-groups  readily  lose  water,  with  formation  of  aldehydes 
or  ketones:  they  also  possess  most  of  the  properties  characteristic 
of  these  substances  (201).  The  hexahydric  alcohols,  however, 
have  an  exclusively  alcoholic  character,  and  do  not  exhibit  any 
of  the  reactions  of  aldehydes  and  ketones.  It  follows  that  the 
hexahydric  alcohols,  and  hence  the  hexoses,  cannot  contain  two 
hydroxyl-groups  linked  to  a  single  carbon  atom. 

The  possibility  of  the  attachment  of  three  hydroxyl-groups  to 
one  carbon  atom  is  also  excluded,  since,  when  the  production  of 
a  compound  with  such  a  grouping  might  be  expected,  water  is 
always  eliminated,  with  formation  of  an  acid  (79)  : 

OH] 

— COJH. 
IOH 

The  monoses  have  none  of  the  properties  which  distinguish  acids: 
their  aqueous  solutions  do  not  conduct  the  electric  current;  whereas 
the  dissociation-constant  for  an  acid  containing  so  many  OH- 
groups  should  be  considerably  higher  than  for  a  saturated  fatty 
acid,  such  as  acetic  acid  (180) . 

With  calcium  and  strontium  hydroxides,  and  other  bases,  the 
carbohydrates  form  compounds  called  saccharates,  which  are,  there- 
fore, to  be  looked  upon  as  alkoxides  (50). 

It  follows  from  these  considerations  that  the  constitution  of  the 
aldohexoses  cannot  be  other  than  that  given  above,  and,  since  the 
same  method  of  proof  is  applicable  to  each  member,  they  must  all 
have  the  same  constitutional  formula,  and  are  therefore  stereoiso- 
merides.  This  is  due  to  the  presence  in  the  molecule  of  asymmetric 
carbon  atoms:  an  aldohexose  has  four  such  atoms,  indicated  by 
asterisks  in  the  formula 

CH2OH  •  CHOH  •  CHOH .  CHOH .  CHOH  •  C  . 


262  ORGANIC   CHEMISTRY.  [§206 


Methods  of  Formation  of  the  Monoses. 

206.   1.  From  the  poly oses,  by  hydrolysis ;   that  is,  decomposi- 
tion with  addition  of  water. 

2.  From  the  corresponding  alcohols,  by  the  action  of  oxidizing 
agents,  such  as  nitric  acid.     Arabitol,  C5H1205,  yields  arabinose, 
CsHioOs;    xylitol  yields  xylose;    mannitol  yields  mannose;    etc. 

When  glycerol  is  carefully  oxidized  with  hydrogen  peroxide  in 
presence  of  ferrous  salts,  or  with  bromine  and  sodium  carbonate, 
a  syrup-like  liquid  called  glycerose  is  obtained,  with  the  four  reac- 
tions typical  of  monoses  (203).  Prepared  by  the  first  method,  it  is 
essentially  glyceraldehyde  (I.);  by  the  second  method,  only  di- 
hydroxyacetone  (II.)  is  produced.  Both  compounds  yield  the  same 
osazone,  glycerosazone  (III.),  a  substance  crystallizing  in  yellow 
leaflets,  melting  at  131°: 

CH2OH  CH2OH  CH2OH 

CHOH  CO  C=N-NH-CjH, 

*H  CH2OH  C=N-NH-C.H. 

°0  H 

I.  II.  HI- 

In  accordance  with  the  nomenclature  already  indicated,  glycerose 
is  a  triose. 

When  sorbose-bacteria  are  cultivated  in  a  solution  of  glycerol, 
the  final  product  obtained  by  the  action  of  the  atmospheric  oxygen 
is  dihydroxyacetone.  These  bacteria  can  also  oxidize  other  poly- 
hydric  alcohols  to  ketoses. 

3.  From    bromo-compounds    of    aldehydes,    by   exchange    of 
bromine  for  hydroxyl,  which  can  be  effected  by  cold  baryta-water. 

In  this  manner  the  simplest  member  of  the  sugars,  glycolose  or 

TT 

glycottaldehyde,  CH2OH'C  Q,  is  obtained  from  monobromoaldehyde, 

TT 

CH2Br»Co:   it  shows  all  the  reactions  of  the  monoses.     Glycolose 

crystallizes  well,  and  melts  with  decomposition  at  about  97°.     It 
polymerizes  readily,  and  is  volatile  with  steam. 

The     addition     of     bromine     to     acraldehyde     (141)     yields 

CH2Br»CHBr-CQ,  which  is  converted  by  the  action  of  baryta- 
water  into  glyceraldehyde. 


§206]  MONOSES.  263 

4.  From  formaldehyde,  by  the  action  of  lime-water  (alclol- 
condensation).  The  crude  condensation-product,  called  formose, 
is  a  sweet,  syrup-like  substance  :  it  consists  of  a  mixture  of  com- 
pounds of  the  formula  C6H12O6.  In  this  reaction,  six  molecules  of 
formaldehyde  undergo  the  aldol-condensation  (106)  : 

^-—  H      ,  __  H    ^  -  H     ^  -  H 

/      I  /      I  -r     i  /     i  > 

H2CO  +  HCO  +  HCO  +   HCO  +   HCO 

TT  c^c\3     ~**-*- 


4 

By  the  aid  of  sunlight  and  moisture,  plants  are  able  to  convert 
the  carbon  dioxide  of  the  atmosphere  into  starch,  a  polyose  of  the 
formula  (C6H1006)X.  The  reaction  may  be  represented  empirically, 
thus: 

6CO2+5H2O  =  C6Hio05+602. 

The  botanical  term  for  this  reaction  is  photosynthesis,  and  the 
process  is  of  the  highest  importance  for  every  form  of  life,  since 
without  it  the  existence  of  life  would  be  impossible.  VON  BAEYER 
explains  the  mechanism  of  the  synthesis  by  assuming  preliminary 
reduction  of  carbon  dioxide  to  formaldehyde,  CH2O,  followed  by 
condensation  of  the  aldehyde  to  form  a  monose,  and  the  ultimate 
conversion  of  the  monose  into  a  polyose. 

Under  the  influence  of  ultraviolet  light,  moist  carbon  dioxide  is 
reduced  to  formaldehyde.  Since  photosynthesis  is  promoted  prin- 
cipally by  yellow  light,  but  not  by  blue  or  ultraviolet  light,  the 
formation  of  aldehyde  in  the  process  must  be  due  to  a  different  cause. 

CURTIUS  has  demonstrated  the  presence  of  small  quantities  of 
formaldehyde  in  fresh  leaves. 

A  hexose  can  also  be  obtained  from  glyceraldehyde,  two  mole- 
cules of  which  yield,  by  the  aldol-condensation,  one  molecule  of  the 
hexose.  This  hexose  is  called  acrose,  on  account  of  its  relation  to 
acraldehyde,  from  which  glyceraldehyde  can  be  obtained  by 
method  3.  Acrose  is  a  constituent  of  formose,  and,  like  all 
compounds  prepared  by  purely  chemical  synthesis,  is  optically 
inactive. 

5.  A  very  important  general  method  for  the  conversion  of  an 
aldose  into  another  containing  one  more  carbon  atom  in  the  mole- 
cule is  the  formation  of  an  addition-product  with  hydrocyanic 


264  ORGANIC  CHEMISTRY.  [§207 

acid.     An  aldohexose  yields  a  cyanohydrin  which  is  converted  on 
hydrolysis  into  a  monobasic  acid  containing  seven  C-atoms, 

r  ft  a 

CH2OH.CHOH.CHOH.CHOH.CHOH-CHOH.COOH. 

1  234567 

The  ^-hydroxyl-group  reacts  easily  with  the  carboxyl-group,  form- 
ing a  lactone, 

CHOH  -  CHOH  -  CHOH  -  CH  -  CHOH  .  CHOH  •  CO. 


In  aqueous  solution,  these  lactones  can  be  reduced  by  sodium-amal- 
gam to  the  corresponding  aldehydes,  the  aldoses. 

The  great  importance  of  this  synthesis  consists  in  the  theore- 
tical possibility  of  obtaining  from  the  lower  members,  step  by  step,. 
aldoses  with  any  desired  number  of  C-atoms  in  the  molecule,  by 
repeated  application  of  the  cyanohydrin-syn  thesis,  and  reduction 
of  the  lactone  thus  obtained.  It  has  thus  been  possible  to  prepare 
nonoses,  with  nine  C-atoms,  by  conversion  of  an  aldohexose  into  a 
heptonic  acid,  the  lactone  of  which  can  then  be  reduced  to  a  heptose. 
This  compound  can  be  converted  into  an  octose,  and  the  latter  into- 
a  nonose,  by  the  same  process. 

I.  MONOSES. 
Pentoses. 

207.  Reference  has  already  been  made  to  the  dioses  and  trioses 
(202).  Tetroses  can  be  obtained  by  the  oxidation  of  pentonic 
acid,  in  the  form  of  its  calcium  salt,  by  means  of  hydrogen  peroxide, 
a  small  quantity  of  ferric  acetate  being  used  as  a  catalyst  : 

CH2OH-  CHOH.  CHOH.  CHOH-  COOH+O= 

Pentonic  acid 

=  CH2OH.CHOH.CHOH-c5+CO2+H20. 

Tetrose 

Also  pentoses  can  be  obtained  from  hexoses  by  this  method. 

A  number  of  different  pentoses  have  been  identified,  among. 
them  arabinose  and  xylose,  both  of  which  are  present  in  many  plants 
as  polyoses,  called  pentosans. 


•I  207]  MONOSES.  265 

Arabinose  can  be  prepared  by  boiling  gum-arabic  or  cherry-gum 
with  dilute  acids,  but  the  best  method  is  to  hydrolyze  sliced  sugar- 
beet  after  extraction  of  the  sugar,  the  resulting  mixture  of  galac- 
tose  and  arabinose  being  freed  from  galactose  by  fermentation. 
Xylose,  or  wood-sugar,  can  be  obtained  similarly  from  bran,  wood, 
straw,  and  other  substances,  especially  the  shells  of  apricot- 
stones.  Arabinose  and  xylose  can  be  prepared  from  any  plant- 
cells  which  have  been  converted  into  wood,  and  which  show 
the  reactions  of  ligm'n  (228).  The  racemic  modification  of  arabin- 
ose is  present  in  the  urine  of  patients  suffering  from  the  disease 
Jmown  as  pentosuria. 

Arabinose  forms  well-defined  crystals,  melts  at  160°,  and  has 
a  sweet  taste,  its  osazone  melts  at  157°.  Xylose  also  crystallizes 
well,  and  yields  an  osazone  which  melts  at  160°. 

Arabinose  and  xylose  are  aldoses,  and  have  the  same  formula^ 

CH2OH  •  CHOH  •  CHOH .  CHOH  •  CQ  . 

This  constitution  is  proved  by  their  conversion,  on  gentle  oxidation 
with  bromine-water,  into  arabonic  acid  and  xylonic  acid  respectively, 
both  of  which  have  the  formula  CH2OH-  (CHOH)3.COOH,  and  are 
therefore  stereo isomeric.  On  stronger  oxidation,  both  arabinose 
and  xylose  yield  trihydroxyglutaric  acid,  COOH-  (CHOH)3.COOH, 
the  constitution  of  which  follows  from  its  reduction  to  glutaric 
acid.  The  acid  obtained  from  arabinose  is  optically  active,  and 
that  from  xylose  is  inactive,  so  that  they,  too,  are  stereoisomerides. 
On  reduction,  these  two  pentoses  yield  respectively  arabitol  and 
xylitol,  which  are  stereoisomeric  pentahydric  alcohols.  Arabinose 
and  xylose  can  be  converted  into  hexoses  by  the  cyanohydrin- 
synthesis,  a  proof  that  neither  contains  a  C-atom  in  union  with  more 
than  one  OH-group  (205),  and  that  each  has  a  normal  carbon  chain: 

CH2OH.(CHOH)3.C?  -»  CH2OH.(CHOH)3.CH<°^-» 

Pentose  ^ 

-*  CH2OH-(CHOH)3.CHOH.COOH. 

Hexonic  acid 

This  hexonic  acid  yields  a  lactone  which,  on  reduction,  gives  the 
hexose.  Arabinose  and  xylose  contain  three  asymmetric  C-atoms, 
and  are  optically  active. 


266  ORGANIC   CHEMISTRY.  [§  208 

The  pentoses  cannot  be  fermented.  They  have  one  property 
in  common,  by  which  they  may  be  recognized  and  distinguished 
from  hexoses.  When  boiled  with  dilute  sulphuric  acid,  or  hydro- 
chloric acid  of  sp.  gr.  1*06,  the  pentoses  and  their  polyoses  form 
a  volatile  compound,  furfur  aldehyde,  C5H4O2  (393),  which,  on 
treatment  with  aniline  and  hydrochloric  acid,  yields  an  intense 
red  dye. 

The  presence  of  the  polyose  of  xylose  can  be  detected  in  such  a 
substance  as  straw  by  distillation  with  hydrochloric  acid  of  sp.  gr. 
1*06.  With  aniline  and  hydrochloric  acid,  the  distillate  gives  an 
intense  red  coloration,  and  with  phenylhydrazine  yields  a  phenyl- 
hydrazone  very  sparingly  soluble  in  water.  Both  these  reactions 
indicate  the  presence  of  furfuraldehyde. 

Hexoses. 

208.  The  hexoses  are  colourless  compounds  of  sweet  taste, 
which  are  difficult  to  crystallize,  and  cannot  be  distilled  without 
decomposition.  They  dissolve  readily  in  water,  with  difficulty  in 
absolute  alcohol,  and  are  insoluble  in  ether.  Since  all  the  aldo- 
hexoses  are  stereoisomerides  (205),  their  oxidation-products,  the 
monobasic  and  dibasic  acids,  are  also  stereoisomerides. 

1.  Dextrose  (d-glucose  or  grape-sugar)  is  present  in  many  plants, 
notably  in  the  juice  of  grapes,  and  in  other  sweet  fruits :  it  is  found 
in  the  urine  of  diabetic  patients,  and  in  small  quantities  in  normal 
urine.  It  can  be  obtained  from  many  polyoses:  for  example, 
cane-sugar  is  converted  by  hydrolysis — inversion  (216) — into  a 
mixture  of  dextrose  and  laBvulose  (209),  called  invert-sugar.  The 
technical  preparation  of  dextrose  from  starch,  by  boiling  with  dilute 
acids,  is  likewise  a  case  of  hydrolysis. 

Dextrose  crystallizes  from  water,  or  alcohol,  with  some  diffi- 
culty; the  crystals  obtained  from  methyl  alcohol  contain  no  water 
of  crystallization,  and  melt  at  146°.  It  is  mentioned  in  43  that 
dextrose  can  be  readily  fermented,  producing  chiefly  alcohol  and 
carbon  dioxide.  Natural  dextrose  is  dextro-rotatory:'  a  Isevo- 
rotatory  and  an  optically  inactive  modification  have  been  arti- 
ficially prepared.  The  dextro-rotatory,  laevo-rotatory,  and  optically 
inactive  isomerides  are  respectively  distinguished  by  the  prefixes 
d  (dexter),  I  (loevus),  and  i  (inactive^);  thus,  rf-glucose,  /-glucose, 
i-glucose. 


§  208]  MONOSES.  267 

By  convention,  all  other  monoses  derived  from  a  d-hexose, 
Z-hexose,  or  t-hexose  are  also  distinguished  by  the  letters  d,  I,  or  i, 
even  when  they  possess  a  rotatory  power  opposite  in  sign  to  that 
indicated  by  these  letters.  Thus,  Isevulose  or  ordinary  fructose, 
which  can  be  obtained  from  dextrose  or  d-glucose,  and  is  laevo- 
rotatory,  is  also  called  d-fructose  on  account  of  its  genetic  relation  to 
d-glucose.  The  same  method  of  classification  is  adopted  for  the 
hexahydric  alcohols,  the  hexonic  acids,  and  in  general  for  all  deriva- 
tives of  the  hexoses. 

Dextrose  is  an  aldose,  as  is  proved  by  its  oxidation  to  a  hexonic 
acid,  d-gluconic  acid,  CH2OH.(CHOH)4-COOH:  further  oxidation 
produces  the  dibasic  d-saccharic  acid, 

COOH.(CHOH)4-COOH. 

Saccharic  acid  forms  a  characteristic  potassium  hydrogen  salt  of 
slight  solubility,  which  serves  as  a  test  for  dextrose.  The  substance 
suspected  of  containing  dextrose  is  oxidized  with  nitric  acid:  sac- 
charic acid  is  produced  from  this  hexose,  if  present,  and  can  be  pre- 
cipitated as  potassium  hydrogen  salt  by  addition  of  a  concentrated 
solution  of  potassium  acetate. 

On  reduction,  dextrose  yields  a  hexahydric  alcohol,  d-sorbitol: 
it  also  gives  an  osazone,  d-glucosazone,  which  is  soluble  with  diffi- 
culty in  water,  and  crystallizes  in  yellow  needles  which  melt  at 
205°. 

Solutions  of  dextrose  and  many  other  sugars  furnish  examples  of 
a  phenomenon  called  mutarotation.  When  freshlv  dissolved,  such 
substances  have  a  rotatory  power  other  than  that  possessed  by  them 
after  the  lapse  of  a  comparatively  short  interval  of  time.  Thus,  an 
aqueous  solution  of  dextrose  at  first  produces  a  rotation  [a]D  =  110°: 
after  some  hours  it  produces  a  constant  rotation  [«]D=52-5°.  The 
attainment  of  a  constant  rotatory  power  is  much  hastened  by  boiling 
the  solution,  and  is  effected  at  once  by  addition  of  a  small  quantity 
of  caustic  potash  or  ammonia. 

The  explanation  of  this  phenomenon  must  be  sought  in  the  par- 
tial conversion  of  the  dextrose  or  other  sugar  into  another  modifica- 
tion of  different  rotatory  power.  When  the  rotation  has  become 
constant,  there  is  equilibrium  between  the  two  modifications. 

TANRET  has  prepared  three  different  crystalline  modifications  of 
dextrose,  denoted  by  a,  /?,  and  s.  Ordinary  dextrose  is  the  a-modi- 
fication  :  it  crystallizes  with  one  molecule  of  water.  When  dissolved 


ORGANIC   CHEMISTRY.  [§  2C8 

quickly  in  cold  water,  the  solution  produces  a  rotation  [«]£>  =  110°. 
When  the  solid  a-form  is  heated  for  some  days  at  105°,  it  is  changed 
to  the  /?-form.  In  aqueous  solution  the  /^-modification  at  first  only 
rotates  the  plane  through  [a]0  =  19°:  when  allowed  to  remain  for 
some  time,  or  boiled,  or  mixed  with  a  trace  of  alkali,  the  rotation 
rises  to  [«]D  =  52  •  5°.  When  dissolved  in  water,  the  ^-modification 
at  once  causes  a  rotation  [afj0=52-5°,  indicating  that  it  is  not  an 
independent  form,  but  a  mixture  in  equilibrium  of  the  a-modifica- 
tion  and  /^-modification. 

TANRET  has  proved  by  experiment  that  this  surmise  is  correct. 
A  very  concentrated  solution  of  the  ^-modification  was  made,  and 
crystallized  at  0°.  When  a  solution  of  the  crystals  thus  obtained 
was  prepared  at  a  low  temperature,  its  rotation  was  diminished  by 
addition  of  a  small  quantity  of  ammonia,  proving  that  the  crystals 
belonged  to  the  ct-modification.  If  the  £-form  is  a  mixturo  of  tho 
^-modification  and  the  /^-modification,  the  latter  must  have  remained 
in  solution  in  the  mother-liquor,  and  addition  of  alkali  should  increase 
the  rotation  of  this  residual  solution.  Experiment  has  proved  that 
alkali  has  this  effect. 

The  results  of  these  researches,  in  conjunction  with  other  facts, 
have  led  to  the  adoption  of  a  somewhat  modified  type  of  constitu- 
tional formula  for  the  monoses  (217). 

With  a  small   quantity  of  water,  dextrose  yields  a  colourless 
;syrup  used  in  the  preparation  of  liqueurs  and  of  confectionery. 

The  mechanism  of  the  formation  of  ethyl  alcohol  and  carbon  dioxide 
by  the  fermentation  of  dextrose  is  probably  best  explained  by  assuming 
alterations  in  the  relative  positions  occupied  by  the  hydroxyl- 
groups  and  hydrogen  atoms.  It  may  be  supposed  that  elimination 
of  water  in  the  usual  manner  first  takes  place,  being  followed  by 
the  migration  of  one  hydrogen  atom.  These  changes  involve  the 
transformation  of  the  group  — CHOH-CHOH —  by  abstraction  of 
water  into  — OH -C(OH)— ,  which  then  changes  to  — CH2.CO— . 
The  result  is  the  same  a,s  that  produced  by  an  exchange  of  position 
between  hydrogen  and  hydroxyl,  followed  by  elimination  of  water: 

— CHOH-CHOH >—  CH2-C(OH)2 >— CH2.CO— . 

Analogous  phenomena  are  known,  among  them  the  formation  of 
acraldehyde  from  glycerol  (151),  of  pyroracemic  from  tartaric  acid 
(231),  and  of  oxalacetic  acid,  COOH-CO-CH2-COOH,  from  tartaric 
.acid. 

Methylglyoxal,   which   was   isolated   as    osazone,  is  an  inter- 


§  209]  MONOSES.  269 

mediate  decomposition-product  in  the  interaction  of  dextrose  and 
dilute  alkalis,  as  indicated  in  the  following  scheme  : 

CH?OH  -CHOH  -CHOH  -CHOH  -CHOH  -CQ  -> 

(Migration  of  H  and  OH) 

->  CH3.C(OH)2.C(OH)2.CH2.CHOH.c9  -> 
H     OH 

(Decomposition  with  addition  of  IF^O) 

-»CH3.CO.CQ     and    CH2OH.CHOH.C^  —  H2O  ->  CH3.CQ.C^ 

Methylglyoxai  Methylglyoxal  ' 

Lactic  acid  has  been  identified  as  an  intermediate  product  in 
alcoholic  fermentation,  and  may  be  regarded  as  derived  from 
methyiglyoxal  in  accordance  with  the  scheme 

CHS-C(OH)2.QQ  -*  CH3.CHOH.CQH, 

Methylglyoxal  Lactic  acid 

resulting  from  a  change  of  position  between  hydroxyl  and  hydrogen. 
The  lactic  acid  then  loses  carbon  dioxide,  yielding  ethyl  alcohol: 

CH3.CHOH.CO2H  =  CH3-CH2OH+CO2. 

It  is  not  improbable  that  two  enzymes  play  a  part  in  these 
reactions.  One  of  them  may  occasion  the  interchange  of  position 
leading  to  the  formation  of  lactic  acid;  the  other  may  effect  the 
decomposition  of  the  lactic  acid  into  alcohol  and  carbon  dioxide,. 

The  conversion  of  dextrose  into  butyric  acid  by  the  butyric 
fermentation  can  also  be  explained  by  assuming  the  intermediate 
formation  of  lactic  acid,  and  its  subsequent  transformation  into 
formic  acid  and  acetaldehyde.  Condensation  of  acetaldehyde  pro- 
duces aldol,  which  yields  butyric  acid  by  transposition  of  H  and  OH  : 


Aldol  Butyric  acid 

209.  Lcevulose  (d-fructose  or  fruit-sugar)  is  present  along  with 
dextrose  in  most  sweet  fruits.  It  is  a  constituent  of  in  vert  -sugar 
(216)  ,  and  of  honey,  which  is  chiefly  a  natural  invert-sugar.  When 
hydrolyzed,  inulin,  a  polyose  contained  in  dahlia-tubers,  yields 
only  laevulose,  just  as  starch  yields  dextrose.  laevulose  crystal- 
lizes with  difficulty,  being  readily  soluble  in  water,  although  less 
so  than  dextrose.  It  is  laevo-rotatory,  and  can  be  fermented. 


270  ORGANIC  CHEMISTRY.  [§209 

Lsevulose  is  a  type  of  the  ketoses,  but  few  of  which  are  known. 
Its  formula,  CH2OH.(CHOH)3.CO.CH2OH,  is  inferred  from  the 
following  considerations.  First,  when  oxidized  with  mercuric 
oxide  in  presence  of  baryta-water,  it  is  converted  into  glycollic 
acid,  CH2OH-COOH,  and  trihydroxyglutaric  acid, 

COOH  •  (CHOH)3  •  COOH. 

Since  oxidation  takes  place  in  the  carbonyl-group,  the  production 
of  these  acids  necessitates  the  adoption  of  this  constitutional 
formula.  Second,  application  of  the  cyanohydrin-svnthesis  to  a 
compound  of  this  constitution  would  yield  a  heptonic  acid  with 
the  formula 

CH2OH.(CHOH)3.C(OH).CH2OH. 

I 
COOH 

That  the  heptonic  acid  obtained  from  Isevulose  has  this  consti- 
tution, is  proved  by  heating  it  at  a  high  temperature  with 
hydriodic  acid,  whereby  all  the  hydroxyl-groups  are  replaced  by 
hydrogen,  and  a  heptylic  acid  is  formed.  This  acid  is  identical 
with  the  synthetic  methyl-r\-butylacetic  acid  (233,  2), 

CH3.(CH2)3.CH.CH3 
COOH 

The  osazone  of  Isevulose  is  identical  with  that  of  dextrose.  A 
comparison  of  the  formula  of  dextrose, 

CH2OH  -  (CHOH)3  -  CHOH  -  CQ  , 

with  that  of  laevulose,  CH2OH.(CHOH)3.CO-CH2OH,  shows  that 
the  two  osazones  can  only  be  identical  if  the  a-C-atom  of  dextrose, 
and  the  terminal  C-atom  of  lasvulose,  respectively  unite,  after  for- 
mation of  the  hydrazone,  with  the  second  phenylhydrazine-residue: 
that  is,  when  in  both  cases  this  reaction  takes  place  at  a  C-atom 
directly  linked  to  a  carbonyl-group.  For  this  reason,  it  is  assumed 
that  the  formation  of  an  osazone  always  results  in  the  union 
of  two  phenylhydrazine-residues  with  neighbouring  C-atoms. 
d-Glucosazone,  or  d-fructosazone,  has  therefore  the  constitution 


210]  MONOSES.  271 

CH2OH 
(CHOH)3 
C=N-NH.C6H5 
C=N.NH.C6H5 
H 


Methylpheriylhydrazine,  r  TT3>N-NH2,    yields    osazones    with 

vygXJ-S 

ketoses  only,  but  converts  aldoses  into  colourless  hydrazones, 
readily  separated  from  the  intensely  yellow  osazones.  This  reagent 
is  a  valuable  aid  in  the  detection  of  ketoses. 

When  osazones  are  carefully  warmed  with  hydrochloric  acid,  two 
molecules  of  phenylhydrazine  are  eliminated,  with  formation  of  com- 
pounds, osones,  containing  two  carbonyl-groups.  For  example, 
d-glucosazone  yields  d-glucosone, 

CH.OH-(CHOH)r/CO-C^. 

The  osones  can  be  reduced  by  treatment  with  zinc-dust  and  acetic 
acid,  and  it  is  found  that  addition  of  hydrogen  always  takes  place 
at  the  terminal  C-atom.  d-Glucosone  yields 

CH2OH  •  (CHOH  )a  •  CO  • 


The  reaction  affords  a  means  of  converting  aldoses  into  ketoses: 
Aldose  —  >  Osazone  —  >  Osone  —  >  Ketose. 

Inversely,  an  aldose  can  be  obtained  from  a  ketose.  On  reduction, 
the  latter  yields  a  hexahydric  alcohol,  which  is  converted  by  oxida- 
tion into  a  monobasic  hexonic  acid.  This  substance  loses  water, 
yielding  the  corresponding  lactone,  which  on  reduction  gives  the 
aldose  : 

Ketose  —  >  Hexahydric  Alcohol  —  >  Hexonic  Acid  —  >  Lactone  -»  Aldose. 


210.  d-Mannose  is  an  aldose,  and  is  present  as  a  polyose  in  the 
vegetable-ivory  nut:  it  is  also  obtained  by  the  careful  oxidation 
of  the  hexahydric  alcohol  mannttol,  found  in  several  plants. 
d-Mannose,  a  hard,  amorphous,  hygroscopic  substance,  can  be  readily 
fermented,  and  is  very  soluble  in  water.  It  yields  a  characteristic 
hydrazone  which  melts  at  195°-200°,  and,  unlike  the  hydrazones 


272  ORGANIC  CHEMISTRY.  [§210 

of  the  other  monoses,  dissolves  with  difficulty  in  water.  On  oxi- 
dation, d-mannose  is  first  converted  into  the  monobasic  d-mannonic 
acid,  CH2OH-  (CHOH)4-COOH,  and  then  into  the  dibasic  d-manno- 
saccharic  acid,  COOH-(CHOH)4.COOH.  It  yields  dextrose  by 
a  method  generally  applicable  to  the  conversion  of  aldoses  into 
their  stereoisomerides.  For  this  purpose,  it  is  first  converted  into 
d-mannonic  acid.  On  boiling  the  solution  of  this  substance  in 
quinoline  (400),  it  is  partly  transformed  into  the  stereoisomeric 
d-gluconic  acid,  the  lactone  of  which  can  be  reduced  to  dextrose,. 
Inversely,  d-gluconic  acid  is  partly  changed  into  d-mannonic  acid, 
by  boiling  its  quinoline  solution,  so  that  dextrose  can  thus  be  con- 
verted into  d-mannose. 

Mannonic  acid  is  one  of  the  intermediate  products  in  EMIL 
FISCHER'S  synthesis  of  dextrose.  He  converted  glyceraldehyde  into 
acrose  (206,  4),  and  this  into  i-mannitol,  by  reduction  with  sodium- 
amalgam.  On  oxidation,  t-mannitol  yields  first  i-mannose,  and  then 
t-mannonic  acid,  which  can  be  resolved,  by  means  of  its  strychnine 
salt,  into  its  optically  active  modifications.  When  the  d-mannonie 
acid  thus  obtained  is  heated  with  pyridine,  it  is  converted  into 
c?-gluconic  acid,  the  lactone  of  which,  on  reduction  with  sodium- 
amalgam,  yields  dextrose. 

The  stereoisomerism  of  d-mannose  and  dextrose,  as  well  as  of 
d-mannonic  acid  and  d-gluconic  acid,  is  occasioned  only  by  different 
grouping  round  the  a-C-atom,  since  the  osazone  of  d-mannose  is 
identical  with  that  of  dextrose.  As  this  has  the  constitution 

a    H 
CH2OH  •  CHOH  -  CHOH  •  CHOH  •  C— C=N  -  NH .  C6H5, 

N.NH.C6H5 

these  osazones  can  only  be  identical  when  the  residue 
CH2OH .  (CHOH)2  •  CHOH- 

in  d-mannose  and  dextrose  is  also  identical:  their  stereoisomensrr> 
can  then  only  result  from  a  difference  in  the  arrangement  of  the 
groups  linked  to  the  a-C-atom. 

So  far  as  the  transformations  of  the  monobasic  hexonic  acids 
when  boiled  with  quinoline  or  pyridine  have  been  studied,  it  has 


§§  211, 212]  MONOSES.  273 

always  been  found  that  the  alteration  takes  place,  as  in  the  above 
instance,  at  only  one  C-atom,  and  this  the  one  adjoining  the 
aldehydo-group,  the  a-C-atom. 

211.  d-Galactose  can  be  obtained  by  the  hydrolysis  of  lactose,  or 
by  tae  oxidation  of  the  hexahydric  alcohol  dulcitol,  which  occurs  in 
certain  plants.  d-Galactose  is  crystalline,  melting  at  168°;  it  is 
strongly  dextro-rotatory,  is  capable  of  undergoing  fermentation, 
and  exhibits  mutarotation.  Galactose  is  proved  to  be  an  aldose 
by  its  conversion,  on  oxidation,  into  the  monobasic  d-galactonic 
acid,  C6H12O7.  Further  oxidation  yields  the  sparingly  soluble 
dibasic  mucic  acid,  COOH.(CHOH)4.COOH,  which  is  optically  in- 
active, and  cannot  be  resolved  into  optically  active  components: 
its  formation  serves  as  a  test  for  c?-galactose.  This  is  carried  out 
by  oxidizing  the  hexose  under  examination  with  nitric  acid. 

Their  conversion  into  Iwvulic  acid  (234),  on  treatment  with 
hydrochloric  acid,  constitutes  a  general  reaction  for  the  hexoses. 
Brown,  amorphous  masses,  known  as  humic  substances,  are  pro- 
duced at  the  same  time.  Laevulic  acid  can  be  identified  by 
.means  of  its  silver  salt,  which  dissolves  with  difficulty,  and  yields 
characteristic  crystals. 

The  identification  of  the  constituents  of  a,  mixture  x>f  mrmnsps — 

"can  often  be  read ily  effected  by  the  aid  of  phenylhydrazine  and 

its  substitution-products  (310),  the  tendency  of  each  monose  to 
form  a  phenylhydrazone  or  osazone  depending  on  the  particular 
hydrazine-derivative  employed.  Thus,  from  a  solution  containing 
arabinose  and  dextrose  unsymmetrical  methylphenylhydrazine, 
C6H5N(CH3)-NH2,  dissolved  in  acetic  acid  precipitates  aro,"~L:ose- 
methylphenylhydrazone.  If  this  is  filtered  off  and  the  liquid 
warmed  after  addition  of  an  acetic-acid  solution  of  phenylhydra- 
zine, phenylglucosazone  crystallizes  out. 

Stereochemistry  of  the  Monoses. 

212.  It  was  stated  (205)  that  all  the  aldohexoses  and  aldopen- 
toses  have  the  same  structure,  and  that,  in  consequence,  their 
isomerism  must  be  stereoisomerism.  Although  it  would  be  beyond 
the  scope  of  this  book  to  deduce  the  configuration  of  all  the  pentoses 
and  hexoses  mentioned  here,  it  is  desirable  to  indicate  how  this  is 
determined  for  such  compounds;  that  is,  for  those  containing 
several  asymmetric  carbon  atoms  in  the  molecule. 


274  ORGANIC   CHEMISTRY.  [§212 

It  was  mentioned  (188)  that  the  presence  of  two  dissimilar  asym- 
metric C-atoms  in  a  molecule  causes  the  existence  of  a  greater  num- 
ber of  stereoisomerides  than  that  of  two  similar  asymmetric  C-atoms. 
It  will  be  seen  from  a  projection-formula  that  the  principle  applies  to 
a  greater  number  of  asymmetric  C-atoms  in  the  molecule.  The 
projection-formula  for  two  aldopentoses, 

CH2OH  CH2OH 


HO 

HO 

HO 


H  H- 

-H     and     H- 
-H  H- 


OH 

-OH, 
OH 


cannot  be  made  to  coincide  by  rotation  in  the  plane  of  the  paper 
(190):  the  aldopentoses,  therefore,  are  not  identical.  The  corre- 
sponding trihydroxyglutaric  acids 

COOH  COOH 


HO 

HO— 
HO 


-H  H OH 

-H    and 


*- H 

COOH 


are,  however,  identical,  since  their  projection-formulae  can  be  made 
to  coincide.  In  these  compounds  the  asymmetric  C-atoms  1  and  3 
are  similar,  while  in  the  pentoses  they  are  dissimilar. 

Assuming  that  the  determination  of  the  configuration  of  a  tri- 
hydroxyglutaric acid  is  possible,  and  that  it  leads  to  the  projection- 
formula  given  above,  it  follows  that  the  pentose  from  which  this  acid 
is  obtained  by  oxidation  must  have  one  of  the  above  configurations, 
and  that  all  others  are  excluded.  It  thus  only  remains  to  distinguish 
between  these  two  configurations, 

In  order  to  determine  the  stereo  chemical  structure  of  a  pentose, 
it  is,  therefore,  first  necessary  to  determine  that  of  the  corresponding 
trihydroxyglutaric  acid.  The  optical  behaviour  of  these  acids  affords 
a  means  of  determining  their  stereochemical  structure.  Xylose, 
which  is  optically  active,  is  converted  by  oxidation  into  an  optically 
inactive  trihydroxyglutaric  acid  which  melts  at  152°.  Since  an 
optically  inactive  substance  is  here  obtained  from  an  optically  active 
one,  not  from  a  racemic  compound,  the  inactivity  must  be  due  to 
intramolecular  compensation,  a  fact  which  must  find  expression  in 
the  configuration  allotted  to  this  particular  trihydroxyglutaric  acid. 
The  projection-formula  of  a  compound  which  is  optically  inactive  on 
account  of  intramolecular  compensation  must  fulfil  this  condition: 
itself  and  its  mirror-image  must  be  capable  of  being  made  to  coincide 


I  212] 


STEREOCHEMISTRY  OF   THE  MONOSES. 


27f> 


by  rotation  in  the  plane  of  the  paper;  that  is,  itself  and  its  mirror- 
image  must  be  identical.  For,  if  it  were  otherwise,  two  enantio- 
morphous  configurations — the  formula  and  its  mirror-image — would 
be  possible,  while  for  intramolecular  compensation  only  one  con- 
figuration is  possible. 

The  above  reasoning  may  be  applied  to  the  determination  of  the 
stereochemical  structure  of  arabinose.  Eight  stereoisomeric  for- 
mulae are  possible  for  a  pentose,  but,  by  arranging  these  in  pairs  of 
mirror-images,  and  taking  one  of  each  pair,  four  different  types  are 
obtained: 
CH2OH  CH2OH  CH2OH  CH2OH 


H 

H— 
H — 


OH         H — 

H— 
— OH      HO — 


OH 


H  — 


OH      HO — 


-H 


HO — 


— OH 
— H 

— H 


H  

—  OH 

HO  — 

-H 

H  — 

—OH 

C5 

IV. 

CJ.J.  . , — 

o  ^o  uo 

I.  II.  III. 

The  mirror-image  of  I.  is  represented  on  p.  274. 

Arabinose  is  converted  by  oxidation  into  an  optically  active  tri- 
hydroxyglutaric  acid.  This  excludes  the  trihydroxyglutarlc  acids 
which  could  be  obtained  from  types  I.  and  IV.,  since  each  of  these 
could  be  made  to  coincide  with  its  mirror-image,  and  thus  would  be> 
optically  inactive: 

COOH 


COOH 


I. 


xa  — 

\JLJL 

OH 

identical  with  its 
mirror-image, 

HO 

OTT 

HO 

c 

;OOH 

C 

^OOH 

COOH 

COOH 

H 


IV.     H< 


H- 


OH 


identical  with  its 
mirror-image, 


COOH 


HO -H 

H-         —OH. 
HO -H 

COOH 


The  fact  that  by  the  aid  of  the  cyanohydrin-synthesis  arabinose 
can  be  converted  into  a  mixture  of  dextrose  and  mannose,  which  on 
oxidation  yields  the  optically  active  saccharic  acid  and  mannosac- 
charic  acid,  enables  a  choice  between  types  II.  and  III.  to  be  made. 

TT  TT 

Since  in  the  cyanohydrin-synthesis  only  the  group  C     in 


276 


ORGANIC  CHEMISTRY. 


[§213 


is  altered,  the  configuration  of  the  rest  of  the  C-atoms  remaining 
unchanged,  saccharic  acid  and  mannosaccharic  acid  must  have  tho 
stereochemical  structure 


COOH 


COOH 


H 
HO 
HO 


r- 

1 

1 

OH 
OH 
H 
H 


or 


OH 

OH 

HO 

OH 

H. 

COOH 

Neither  of  these  can  be 


COOH 

if  arabinose  is  represented  by  formula  II. 

made  to  coincide  with  its  mirror-image,  so  that  formula  II.  is  assumed 

to  represent  arabinose.     Formula  III.  is  excluded,  since  otherwise 

one  'of  the  acids  mentioned  above  must  have  the  stereochemical 

constitution 

COOH 


HO 
H 


— 

OH 
H   , 
H 
OH 


COOH 


which  is  identical  with  its  mirror-image :  one  of  the  acids  would  then 
be  optically  inactive,  which  is  not  the  case. 

Arabinose  has,  therefore,  a  formula  of  the  type  II.,  but  it  is  still 
uncertain  whether  it  should  be  represented  by  the  formula  given 
above,  or  by  its  mirror-image. 

Important  aid  in  the  determination  of  configuration  is  furnished 
by  the  building-up  and  the  breaking-down  of  the  monose  molecules. 
Thus,  oxidation  of  erythrose  yields  mesotartaric  acid,  and  this  fact 
establishes  the  grouping  round  the  central  C-atoms  of  this  tetrose. 
Since  erythrose  is  a  decomposition-product  of  d-arabinose,  this 
reaction  affords  a  partial  insight  into  the  configuration  of  that 
pentose.  As  already  indicated,  synthesis  by  the  cyanohydrin- 
method  enables  the  grouping  in  the  hexoses  to  be  inferred  from  the 
known  configuration  of  the  pentoses. 

II.  DIOSES. 

213.  Most   of  the  dioses    (or  biases)    known   are   exclusively 
derived  from  hexoses,  and  therefore,  have  the  formula 


§214]  DIOSES.  277 

Dioses  hydrolyzable  to  a  pentose  and  a  hexose  are  of  very 
rare  occurrence.    Hydrolysis  of  vicianin,  a  glucoside  present  in  the  , 
seed  of  the  vetch  (Vicia  angustifolia)  ,  yields  hydrocyanic  acid,, 
benzaldehyde,  and  a  diose,  vicianose,  built  up  from  dextrose  and 
Z-arabinose;  as  is  proved  by  its  hydrolysis: 


GI  i  H2oOio  +  H2O 

Vicianose  Dextrose  J-Arabinose 

Apiin,  a  glucoside  present  in  parsley,  is  converted  by  the  action 
of  acids  into  a  diose,  transformed  by  further  hydrolysis  into 
dextrose  and  apiose,  a  pentose  with  a  branched  carbon  chain, 
as  is  proved  by  its  oxidation  to  isovaleric  acid. 

The  hydrolysis  can  be  effected  not  only  by  boiling  with  dilute 
acids,  but  also  by  the  action  of  enzymes  (222).  On  account  of  the 
readiness  with  which  decomposition  with  water  takes  place,  it  is 
assumed  that  the  monoses  from  which  a  diose  is  formed  are  not 
linked  together  through  the  carbon  atoms,  but  through  one  or 
more  oxygen  atoms. 

Hitherto,  all  attempts  to  synthesize  natural  dioses  have  failed. 

EMIL  FISCHER  has,  however,  prepared  artificial  dioses  synthet- 
ically from  monoses,  such  as  dextrose.  Acetic  anhydride  and 
hydrobromic  acid  convert  this  sugar  into  acetobromodextrose,  probably 
with  the  formula 

CH2OAc*-CHOAc-CH.CHOAc-CHOA^.CHBr.  ' 
U       _  0-        -J 

Silver  carbonate  eliminates  bromine  from  this  compound,  two 
molecules  becoming  united  by  an  oxygen  atom.  On  careful  saponi- 
fication  with  barium  hydroxide,  the  eight  acetyl-groups  are  removed, 
and  a  diose  with  reducing  properties  synthesized  (217). 

Maltose. 
214.  Maltose  in  the  crystallized  state  has  the  formula 


and  can  be  prepared  from  starch  by  the  action  of  diastase  (43). 
It  is  an  important  intermediate  product  in  the  industrial  pro- 
duction of  alcohol. 


278  ORGANIC  CHEMISTRY.  [§  215 

Maltose  crystallizes  in  small,  white  needles,  and  is  strongly 
dextro-rotatory.  When  boiled  with  dilute  mineral  acids,  it  yields 
only  dextrose.  It  exhibits  all  the  characteristics  of  the  monosesr 
thus,  it  reduces  an  alkaline  copper  solution;  yields  an  osazone, 
maltosazone  (Ci  2H22Oi  i  -  2H2O  -  2H  +  2C6H5NH  •  NH2) ;  and  it 
can  be  oxidized  to  the  monobasic  maltobionic  acid,  Ci2H22O12r 
which,  on  hydrolysis,  splits  up  into  dextrose  and  d-gluconic  acidr 
CH2OH.  (CHOH)4-COOH. 

These  properties  show  that  maltose  contains  only  one  of  the 
two  carbonyl-groups  present  in  two  molecules  of  dextrose:  thus,  it 
forms  an  osazone  with  two,  instead  of  four,  molecules  of  phenyk 
hydrazine,  and  yields  a  monobasic  instead  of  a  dibasic  acid.  The 
linking  of  the  two  molecules  of  dextrose  must,  therefore,  involve 
in  the  reaction  the  carbonyl-oxygen  of  only  one  molecule.  Such  a 
linkage  between  two  monose  molecules  is  called  a  monocarbonyl- 
bond.  If  this  is  denoted  by  the  sign  < ,  and  a  free  carbonyl-group 
in  a  molecule  by  < ,  then  maltose  can  be  represented  by 

C6Hi1O5<O.C6H1105<. 

Dextrose  Dextrose 

Lactose. 

215.  Lactose  (milk-sugar)  is  present  in  milk,  and  is  prepared 
from  it. 

Whey  is  usually  employed  for  this  purpose:  it  is  the  liquid  which 
remains  after  the  cream  has  been  separated  and  the  skimmed  milk 
has  been  used  for  making  cheese.  In  these  processes  the  milk  is 
deprived  of  most  of  its  fats  and  proteins ;  the  whey  contains  nearly 
all  the  lactose,  and  a  large  proportion  of  the  mineral  constituent?  of 
the  milk.  The  lactose  is  obtained  by  evaporation,  and  purified  by 
recrystallization. 

Lactose  crystallizes  in  well-defined,  large,  hard  crystals.  It 
has  not  such  a  sweet  taste  as  sucrose,  and  in  the  mouth  resembles 
sand,  on  account  of  the  hardness  of  its  crystals. 

On  hydrolysis,  lactose  splits  up  into  d-galactose  and  dextrose. 
It  shows  the  reactions  of  the  monoses,  and  can  be  proved,  by  a 
method  analogous  to  that  employed  for  maltose,  to  contain  one 
free  carbonyl-group  in  the  molecule:  it  is,  therefore,  made  up  of 
dextrose  and  c?-galactose,  linked  by  a  monocarbonyl-bond.  The 


§§  216, 217]  DIOSES.  279 

free  carbonyl-group  belongs  to  the  dextrose  molecule,  since  lactose 
is  converted  by  oxidation  with  bromine-water  into  lactobionic  acid, 
which  is  converted  by  hydrolysis  into  c?-galactose  and  d-glucon.ic 
acid.  Lactose  is,  therefore,  represented  by 

C6H1105<O.C6H1105<. 

d-Galactose  Dextrose 

Sucrose. 

216.  Sucrose  (cane-sugar  or  saccharose]  is  present  in  many  plants, 
and  is  prepared  from  sugar-beet  and  sugar-cane.  It  crystallizes 
well,  and  is  very  soluble  in  water.  It  melts  at  160°,  and  on  cooling 
solidifies  to  an  amorphous,  glass-like  mass,  which  after  a  consid- 
erable time  becomes  crystalline.  When  strongly  heated,  it  turns 
brown,  being  converted  into  a  substance  called  caramel.  On 
hydrolysis,  sucrose  yields  dextrose  and  laevulose  in  equal  propor- 
tions. This  mixture  is  called  invert-sugar,  and  is  laBvo-rotatory, 
since  laevulose  rotates  the  plane  of  polarization  more  to  the  left  (209) 
than  dextrose  does  to  the  right.  Sucrose  itself  is  strongly  dextro- 
rotatory, so  that  the  rotation  has  been  reversed  by  hydrolysis. 
This  is  called  inversion,  a  term  also  applied  to  the  hydrolysis  of 
other  dioses  and  of  polyoses.  Sucrose  does  not  show  the  reactions 
characteristic  of  the  monoses:  thus,  it  does  not  reduce  an  alkaline 
copper  solution,  is  not  turned  brown  by  caustic  potash,  and  does 
not  yield  an  osazone.  Hence,  it  is  evident  that  there  are  no  free 
carbonyl-groups  in  its  molecule;  it  may,  therefore,  be  concluded 
that  both  of  these  have  entered  into  reaction  in  the  union  of  the 
two  monoses.  Such  a  linking  between  two  monoses  is  called  a 
dicarbonyl-bond,  and  is  represented  by  the  sign  <  0  > ;  so  that 
sucrose  has  the  formula 

C6H1105<0>C6H11O5. 

Dextrose  Laevulose 

217.  The  discover}'  that  alcohols  are  able,  under  the  influence  of 
hydrochloric  acid,  to  unite  with  monoses  with  elimination  of  water, 
affords  an  insight  into  the  nature  of  the  monocarbonyl-bond  and 
the  dicarbonyl-bond.  The  substances  thus  formed  are  called  glucos- 
ides,  since  they  are  in  many  respects  analogous  to  the  natural  glucos- 
ides,  substances  which  are  decomposed  into  a  sugar,  and  one  or  more 
compounds  of  various  kinds,  on  boiling  with  dilute  acids.  The  arti- 


280 


ORGANIC  CHEMISTRY. 


[§217 


ficial  glucosides  are  obtained  by  the  action  of  one  molecule  of  an 
alcohol  upon  a  monose  : 


C6H12O6  +  CH3OH  = 


Methyl  glucoside 


These  compounds  were  discovered  by  EMIL  FISCHER,  who  has 
assigned  to  them  a  constitution  analogous  in  some  respects  to  that 
of  the  acetals  (104,  2): 


H 


H!OCH3 


Aldehyde 


Alcohol 


H 


OCH3' 

Acetal 


In  the  formation  of  glucoside,  only  one  molecule  of  alcohol  acts  upon 
the  aldose,  so  that  one  of  the  hydroxyl-groups  of  the  latter  plays  the 
part  of  a  second  alcohol  molecule : 


CH2OH                       CH2OH 

CHOH                        CHOH 

rCHO(H~ 

rCHO  

/?CHOH| 

=    /3CHOH 

aCHOHj 

aCHOH 

CfO~     +H 

OCH8     C—  OCH3 

H                              H 

The  grounds  for  the  assumption  of  this  constitution  are :  first,  these 
glucosides  are  readily  resolved  into  their  components,  which  argues 
against  the  existence  of  a  carbon  bond  between  the  latter;  second, 
the  hydroxyl  of  the  ?-C-atom  is  assumed  to  be  the  one  which  reacts, 
since  other  compounds  containing  the  group  — CHOH -CO—  do  not 
yield  glucosides;  the  a-hydroxyl-group,  therefore,  does  not  react. 
The  r-hydroxyl,  being  attached  to  the  fourth  C-atom  of  the  chain, 
is,  moreover,  the  most  likely  to  enter  into  reaction,  since  a  number 
of  instances  of  similar  behaviour  are  knowji,  such  as  that  of  the  acids 
yielding  lactones  (185). 

The  combination  of  two  monoses  with  elimination  of  one  mole- 
cule of  water  may  be  represented  as  being  analogous  to  the  forma- 
tion of  a  glucoside  from  an  alcohol  and  a  monose.  Maltose  and  lactose, 
which  are  united  by  a  monocarbonyl-bond  and  contain  one  free 
carbonyl-group,  are  combined  thus : 


§218] 


DIOSES. 


281 


CH.OH 

CH2OH         H 

CHOH               u 

CHOH       °O 

rCHOJHT 

CHO—  |     (CHOH)4. 

/?CHOH| 

aCHOH  1 

r 

(CHOH)4  = 

H2O+CHOH 
CHOH 

CH2 

rlrT      4-H 

OCH2 

r  

/ 

H 


H 


By  analogy  the  constitution  of  sucrose,  in  which  laevulose  and  dex- 
trose are  united  by  a  dicarbonyl-bond,  will  be 


CH2OH          CH2OH 

CHOH          sCHO- 

CHO-^ 

«?CHOH 

CHOH 

rCHOH 

CHOH 

04- 

r  

O  af!HoOH 

H 


The  methylglucoside  previously  mentioned  exists  in  two 
isomeric  forms,  denoted  by  a  and  /3,  and  closely  related  to  a-dextrose 
and  ,3-dextrose.  Hydrolysisof  o:-methylglucoside  with  the  enzyme 
maltase  yields  a-dextrose;  that  of  5-methylglucoside  with  emulsin 
forms  /5-dextrose.  These  facts  have  led  to  the  adoption  of  a 
formula  of  lactone-type  for  dextrose : 


CH2OH  •  CHOH  •  CH  .  CHOH  .  CHOH  .  CHOH. 


The  stereoisomerism  of  a  -dextrose  and  ^-dextrose  therefore 
depends  on  variation  in  grouping  at  the  carbon  atom  indicated 
by  an  asterisk  (*).  Similar  reasoning  is  applicable  to  the  other 
monoses.  The  absence  of  an  aldehy  do-group  from  the  constitu- 
tutional  formulae  of  dextrose  and  the  other  monoses  accords  with 
their  inability  to  restore  the  colour  to  SCHIFF'S  reagent  (107). 

Sucrose  forms  compounds  with  bases,  called  saccharates: 
among  them  are  Ci2H22O1i,CaO72H2O  and  C^H^On^CaO, 
which  are  readily  soluble  in  water.  When  the  solution  is  boiled, 


282  ORGANIC   CHEMISTRY.  [§  218 

the  nearly  insoluble  tricalcium  saccharate  Ci2H22Oii,3CaO,3H2O 
is  precipitated. 

Manufacture  of  Sucrose  from  Sugar-beet. 

218.  Sucrose  is  present  in  solution  in  the  cell-fluid  of  the  sugar- 
beet.  The  cell-walls  are  lined  with  a  thin,  continuous  layer  of 
protoplasm,  constituting  a  semi-permeable  membrane,  which  pre- 
vents the  diffusion  of  the  sugar  from  the  ce)ls  at  ordinary  tempera- 
tures. When  placed  in  water  at  80°-90°,  the  protoplasm  is  killed, 
coagulates,  and  develops  minute  ruptures,  through  which  the  cell- 
fluid  can  diffuse.  The  process  is  facilitated  by  cutting  up  the  beet 
into  pieces  2  to  3  mm.  in  thickness.  In  order  to  make  the  diffu- 
sion-process as  complete  as  possible  with  a  minimum  amount  of 
water,  the  slices  are  placed  in  vats  through  which  water  circulates 
in  such  a  manner  that  the  nearly  exhausted  material  is  acted  on 
by  fresh  water,  while  that  which  is  only  partly  exhausted  comes 
into  contact  with  the  solution  already  obtained,  so  that  the  material 
richest  in  sugar  is  treated  with  the  strongest  extract,  and  vice  versa 
(principle  of  the  counter-current).  The  solution  obtained  contains 
12-15  per  cent,  of  sugar,  which  is  about  the  proportion  contained  in 
the  beet  itself. 

Slaked  lime  is  added  to  this  solution y  whereby  a  double  object 
is  attained.  First,  the  free  acids  in  the  juice,  such  as  oxalic  acid 
and  citric  acid,  are  precipitated,  along  with  the  phosphates:  their 
removal  is  necessary,  since  on  concentrating  the  solution  they 
would  cause  inversion.  Second,  proteins  and  colouring  mat- 
ters are  precipitated  from  the  solution.  To  accomplish  these 
objects,  it  is  necessary  to  add  an  excess  of  lime,  part  of  which  goes 
into  solution  as  saccharate.  The  saccharate  is  then  decomposed 
by  a  current  of  carbon  dioxide,  care  being  taken  to  leave  the  liquid 
faintly  alkaline.  The  precipitate  is  separated  by  a  filter-press, 
and  the  filtrate  concentrated.  To  obtain  the  maximum  yield  of 
sugar,  the  concentration  must  take  place  at  a  low  temperature. 
This  is  attained  by  the  use  of  vacuum-pans,  in  which  the  sugar- 
solution  boils  under  diminished  pressure.  The  first  product  of  the 
concentration  is  a  thick  syrup,  more  strongly  alkaline  than  the 
original  solution.  Calcium  carbonate  is  precipitated  by  repeated 
treatment  with  carbon  dioxide  until  the  thick  syrup  is  almost 


§  219]  DIOSES.  283 

neutral.  After  filtration,  the  syrup  is  concentrated  until  crystals 
of  sugar  begin  to  separate.  It  is  then  allowed  to  cool,  when  more 
crystals  are  obtained,  mixed  with  a  syrupy  liquid,  which  is  removed 
in  a  centrifugal  machine.  This  syrup  is  further  crystallized  by 
slow  agitation  with  a  stirring  apparatus,  and  the  crystals  are  again 
separated  by  means  of  the  centrifugal  machine.  The  residual 
syrup  (molasses)  is  worked  up  in  the  preparation  of  alcohol. 

The  sugar  thus  prepared  is  not  pure:  it  is  brown,  and  contains 
a  certain  amount  of  syrup.  The  crude  product  is  purified  by  dis- 
solving it,  decolourizing  with  animal-charcoal,  and  concentrating 
in  vacuum-pans. 


Quantitative  Estimation  of  Sucrose. 

219.  The  great'  practical  importance  of  sucrose  makes  it  de- 
sirable to  have  a  quick  and  accurate  method  of  estimating  it 
quantitatively.  This  is  effected  almost  exclusively  by  examining 
its  aqueous  solution  with  the  polarimeter  (26,  2).  Since  sucrose 
is  strongly  dextro-rotatory  ([a]n=  +66-5°),  a  small  quantity 
produces  an  appreciable  amount  of  rotation,  which,  moreover,  is 
almost  independent  of  the  temperature,  and  for  practical  purposes 
may  be  considered  as  proportional  to  the  concentration.  It  is 
obvious  that  this  method  will  only  yield  accurate  results  when 
no  other  optically  active  substances  are  present  in  the  solution. 
If  such  substances  are  present,  either  they  must  be  removed,  or 
their  effect  taken  into  account.  The  former  method  is  adopted  in 
the  determination  of  the  amount  of  sugar  in  beet.  The  sample  is 
grated  with  a  fine  rasp  to  destroy  the  cell-walls,  and  a  weighed 
quantity  is  made  up  to  a  certain  volume  with  cold  water,  which 
dissolves  not  only  the  sucrose,  but  also  optically  active  proteins. 
The  latter  are  precipitated  with  lead  acetate,  filtered  off,  and  the 
amount  of  rotation  observed. 

When  another  sugar  is  present  in  the  solution  along  with  the 
sucrose,  it  is  necessary  to  proceed  by  the  second  method.  Suppose 
dextrose  is  the  other  sugar  present.  The  rotatory  power  of  the 
solution,  which  will  be  dextro-rotatory,  is  first  determined.  If  it 
be  now  inverted,  the  solution  will  either  diminish  in  dextro-rota- 
tion,  or  will  become  laevo-rotatory,  since  invert-sugar  is  laevo- 


ORGANIC   CHEMISTRY.  [§  220 

•  rotatory.  The  rotatory  power  of  an  invert-sugar  solution  obtained 
from  a  sucrose  solution  of  given  strength  being  known,  these  two 
observations  furnish  the  data  by  which  the  percentage  of  dextrose 
in  cane-sugar  or  beet-sugar  can  be  calculated. 

Velocity  of  Inversion  of  Sucrose. 

220.  The  equation  for  unimolecular  reactions  (95)  may  be 
applied  to  the  inversion  of  a  dilute  solution  of  sucrose.  If  the 
original  amount  of  the  latter  present  was  p,  and  after  a  certain 
time  the  quantity  x  has  been  inverted,  then  the  velocity  s  in  the 
fraction  of  time  immediately  following  can  be  expressed  by  the 
equation 

dx     , 


in  which  k  is  a  constant.  The  inversion  can  be  effected  by  means 
of  different  acids  of  the  same  molecular  concentration:  the 
velocity  of  the  reaction  is  dependent  upon  the  nature  of  the  acid 
employed,  so  that  different  values  are  obtained  for  the  velocity- 
constant  k.  When  the  values  of  this  constant  and  of  the  electrolytic 
dissociation-constant  for  these  acids  are  compared,  they  are  found 
to  be  proportional  to  one  another.  An  acid  which  is  ionized  strongly 
effects  inversion  much  more  rapidly  than  one  but  slightly  ionized, 
from  which  it  follows  that  only  the  ionized  part  of  the  acid  exer- 
cises an  inverting  influence.  Since  only  the  hydrogen  ion  is  com- 
mon to  all  acids,  it  must  be  concluded  that  inversion  is  the  result  of 
the  catalytic  action  of  the  hydrogen  ions.  Inversely,  the  •concentra- 
tion of  the  hydrogen  ion  in  the  solutions  of  acid  salts,  for  example, 
may  be  determined  by  measuring  the  velocity  of  inversion. 

For  an  inversion  effected  by  the  action  of  an  enzyme,  the  equa- 
tion does  not  hold.  This  is  explained  by  the  fact  that  the  reactivity 
of  an  enzyme  depends  on  both  the  concentration  of  the  sucrose  and 
that  of  its  own  in  version  -products,  whereas  the  inverting  power  of 
an  acid  is  independent  of  the  concentration  of  the  latter. 


§221]     FERMENTATION  AND  THE  ACTION  OF  ENZYMES.     2S.> 


Fermentation  and  the  Action  of  Enzymes. 

221.  The  alcoholic  fermentation  of  liquids  is  one  of  the  longest 
known  reactions.  During  the  nineteenth  century  a  number  of 
other  reactions  were  identified  as  fermentation-processes,  such  as 
the  lactic  fermentation  and  butyric  fermentation  of  sugar,  putre- 
factive fermentation,  and  others.  Fermentation-processes  include 
a  number  of  reactions  which  take  place  slowly  and  at  ordinary 
temperatures:  they  are  usually  attended  by  the  evolution  of  a  gas 
and  of  heat,  and  depend  upon  the  action  of  micro-organisms,  such 
as  yeast-cells,  bacteria,  and  schizomycetes. 

The  part  played  by  these  micro-organisms  in  fermentation- 
processes  has  been  the  subject  of  much  diversity  of  opinion.  LIEBIG 
thought  that  yeast  contained  certain  easily  decomposed  ferments, 
and  that  it  was  their  decomposition  which,  as  it  were,  induced  the 
fermentation  of  the  substance.  PASTEUR,  however,  after  a  series 
of  brilliant  researches,  became  convinced  that  fermentation  can 
only  be  brought  about  by  living  yeast-cells,  and  that  the  process 
is,  therefore,  a  physiological  phenomenon;  that  is,  a  complicated 
biological  function  of  these  cells.  Thus,  he  concluded  that  there 
could  be  no  fermentation  without  living  yeast-cells,  a  theory  which 
was  universally  accepted,  LIEBIG'S  supposition  that  the  part  played 
by  the  cells  is  only  a  secondary  one  being  abandoned. 

In  accordance  with  PASTEUR'S  theory,  the  process  of  fermenta- 
tion is  inseparable  from  the  presence  and  propagation  of  yeast- 
cells.  If  it  were  found  possible  to  bring  about  fermentation  with- 
out their  presence,  his  theory  would  fall  to  the  ground.  EDUARD 
BUCHXER  has  effected  this.  He  triturated  fresh  yeast  with  sand, 
whereby  the  cell-walls  were  destroyed.  The  dough-like  mass  was 
submitted  to  great  pressure,  which  expressed  a  liquid  (German, 
Presssaft):  this  expressed  yeast-juice  was  separated  by  nitration 
from  the  cells  still  floating  in  it.  BUCHNER  proved  in  various  ways 
that  this  yeast-juice  contains  neither  living  cells  nor  living  proto- 
plasm: for  instance,  the  yeast  may  be  first  killed  by  the  action  of 
acetone;  the  extract  from  it  can  nevertheless  set  up  active  fermen- 
tation in  a  solution  of  sugar  similarly  to  that  obtained  from  living 
yeast.  The  fermentation  is  caused  by  a  dissolved  substance,  which, 
on  account  of  its  properties,  such  as  coagulation  on  warming,  must 


286  ORGANIC   CHEMISTRY.  [§  222 

be  classed  with  proteins:  it  is  a  kind  of  enzyme,  to  which  BUCHNER 
has  given  the  name  zymase.  The  yeast-cells  only  have  the  func- 
tion of  producing  zymase. 

BUCHNER  has  proved  by  analogous  methods  that  other  fermen- 
tation-processes, such  as  the  lactic  fermentation  and  acetic  fermen- 
tation, are  not  caused  by  the  bacilli  themselves,  but  by  the  enzyme 
they  contain. 

222.  The  chemical  structure  of  the  enzymes  is  still  wholly 
unknown.  Most  of  them  have  not  been  obtained  in  the  pure 
state.  Their  power  of  decomposing  compounds  is  also  not 
understood.  Hitherto,  only  small  insight  has  been  obtained  into 
the  conditions  upon  which  their  action  depends. 

First,  the  enzymes  only  act  at  the  ordinary,  or  at  a  slightly 
elevated,  temperature:  below  the  freezing-point  their  activity  is 
suspended,  but  returns  at  the  ordinary  temperature:  on  heating. 
they  are  decomposed.  Second,  they  are  sometimes  rendered  in- 
active ("  poisoned")  by  the  presence  of  small  quantities  of  certain 
substances,  such  as  hydrocyanic  acid.  Third,  it  is  very  remark- 
able that  a  given  enzyme  can  only  produce  changes  in  a  few  sub- 
stances, and  has  no  action  on  other  similar  compounds.  Thus,  of 
the  different  monoses  containing  two  to  nine  C-atoms,  only  the 
trioses,  hexoses,  and  nonoses  undergo  the  alcoholic  fermentation: 
in  fact,  these  are  the  only  monoses  which,  according  to  their  formula, 
can  be  readily  converted  into  CO2  and  C2H5OH;  for  instance, 


Only  the  monoses  are  capable  of  being  fermented  by  enzymes: 
dioses  must  first  be  converted  into  monoses.  Yeast  contains  an 
enzyme,  inverlase,  which  first  decomposes  sucrose  into  a  mixture 
of  Isevulose  and  dextrose.  This  is  proved  by  the  fact  that  certain 
varieties  of  yeast,  which  do  not  contain  invertase,  are  incapable  of 
fermenting  sucrose:  thus,  Schizosaccharomyces  octosporus,  discov- 
ered by  BEYERINCK,  can  ferment  maltose,  but  not  sucrose.  This 
variety  of  yeast  contains  no  invertase,  but  only  maltase,  the 
enzyme  by  which  maltose  is  hydrolyzed. 

The  aptitude  for  decomposition  by  enzymes,  possessed  by  the 
monoses,  has  been  proved  by  EMIL  FISCHER  to  be  intimately  con- 
nected with  their  stereochemical  configuration.  The  three  naturally 


§222]     FERMENTATION  AND   THE  ACTION  OF  ENZYMES.     287 

occurring  sugars,  dextrose,  d-mannose,  and  laevulose,  are  capable 
of  undergoing  fermentation,  and  there  is  a  great  similarity  in 
their  configurations,  since  they  differ  only  in  the  grouping  round 
two  C-atoms : 


H 


CH2OH 


H 
0 


H  

vy 

-OH 

HO  — 

—  H 

CO 

H  

\j 

—OH 

HO— 

-H 

HO- 

-H 

HO— 

—  H 

HO— 

-H 

H- 

-OH 

H— 

-OH 

H- 

-OH 

HO— 

-H 

H— 

—  OH 

H- 

—OH 

H- 

—OH 

H- 

—  OH 

CH2OH 

UH2OH 

CH2OH 

CH2OH 

Dextrose 

d-Mannose 

Lsevulose 

rf-Galactose 

d-Galactose,  which  is  also  a  natural  product,  has  a  somewhat  dif- 
ferent configuration,  and  is  either  more  slowly  fermented  by  certain 
varieties  of  yeast,  or  not  at  all.  The  mirror-images  of  these  com- 
pounds, /-glucose,  etc.,  are  not  capable  of  undergoing  fermentation. 

The  cause  of  these  phenomena  is  probably  the  asymmetric  struc- 
ture of  the  enzyme  molecule.  Although  these  substances  have  not 
been  obtained  in  the  pure  state,  their  great  resemblance  to  the  pro- 
teins, and  the  probability  of  their  formation  from  them,  render 
their  optical  activity  undoubted :  that  is,  they  are  to  be  looked  upon 
as  built  up  of  asymmetric  molecules.  This  has  led  to  the  hypothesis 
that  there  must  be  a  similarity  in  molecular  configuration  between 
the  enzymes  and  the  substances  which  they  decompose;  and  that 
when  this  similarity  is  wanting,  no  reaction  can  take  place.  EMIL 
FISCHER  appropriately  compares  this  resemblance  in  structure  to 
that  necessary  between  a  lock  and  a  key,  in  order  that  the  latter 
may  pass  the  lock. 

The  application  of  these  views  to  the  chemical  processes  which 
go  on  in  the  more  highly  developed  organisms  leads  to  the  concep- 
tion that  generally  in  reactions  in  which  protei'ns  take  part,  as  is 
undoubtedly  the  case  in  the  protoplasm,  the  configuration  of  the 
molecule  has  the  same  importance  as  its  structure.  Various  phe- 
nomena may  be  thus  explained:  the  sweet  taste  possessed  by  one 
cf  the  optically  active  asparagines,  and  the  absence  of  taste  in  the 
other;  the  different  amounts  to  which  the  three  stereoisomeric 
tartaric  acids  are  oxidized  in  the  body  of  a  dog  fed  with  them ;  the 
fact  that,  on  subcutaneous  injection  of  a  rabbit  with  Z-arabinose  or 


288  ORGANIC  CHEMISTRY.  [§  223 

d-arabinose,  of  the  first  only  7  per  cent.,  of  the  latter  36  per  cent., 
is  excreted  from  the  body  unchanged  in  the  urine;  and  so  on. 


Asymmetric  Synthesis. 

223.  Laboratory-syntheses  effected  with  optically  inactive 
material  always  yield  inactive  compounds:  plants  employ  such 
inactive  material  as  carbon  dioxide  and  water  for  the  synthesis 
of  dextro-rotatory  dextrose  and  numerous  other  optically  active 
compounds.  They  also  produce  optically  active  nitrogenous 
compounds,  such  as  proteins  and  alkaloids,  although  the  nitrogen 
reacts  either  in  the  free  state  or  as  nitric  acid.  Two  problems 
present  themselves  for  solution: 

1 .  The  mode  of  formation  of  the  first  optically  active  substance 
from  inactive  material. 

2.  The  production  of  active  substances  from  inactive  material 
under  the  influence  of  an  already  existing  optically  active  body. 

The  solution  of  the  first  problem  is  still  unattained.  It  has 
been  suggested  that  the  formation  of  the  first  optically  active 
compound  took  place  under  the  influence  of  the  circularly- 
polarized  light  present  at  the  earth's  surface;  but  although  this 
hypothesis  is  plausible,  it  still  lacks  experimental  confirmation. 

More  progress  has  been  made  towards  the  solution  of  the 
second  problem.  EMIL  FISCHER  has  found  that  in  the  cyano- 
hydrin-synthesis  (183)  the  use  of  optically  active  substances  does 
not  always  lead  to  the  production  of  the  two  possible  optical 
isomerides.  An  example  is  furnished  by  mannose,  convertible 
by  the  cyanohydrin-synthesis  into  mannoheptonic  acid.  From 
analogy  with  other  cyanohydrin-syntheses,  the  formation  of  two 
stereoisomeric  mannoheptonic  acids  in  equal  proportions  would 
be  anticipated,  but  only  one  acid  is  obtained.  It  follows  that  the 
building-up  of  a  molecule  from  one  already  asymmetric  can 
continue  in  an  asymmetric  sense.  If  mannose  were  converted  by 
a  triple  application  of  the  cyanohydrin-synthesis  into  a  manno- 
nonose,  the  building-up  being  in  every  instance  in  an  asymmetric 
sense;  and  if  it  were  possible  to  decompose  this  nonose  into  the 
original  hexose  and  a  product  with  three  carbon  atoms,  this  new 
substance  would  also  be  optically  active.  One  optically  active 
molecule  would  thus  have  occasioned  the  formation  of  another. 


§  224]  POLYOSES.  289 

The  formation  of  sugar  in  plants  is  probably  the  result  of  an 
analogous  process.  Dextrose  is  formed  in  the  chlorophyll-grains, 
themselves  composed  of  optically  active  substances.  It  may  be 
assumed  that  prior  to  the  formation  of  sugar  these  substances 
combine  with  carbon  dioxide  or  formaldehyde  (206,  4),  and  that 
the  condensation  to  sugar  is  asymmetric  on  account  of  the  asym- 
metric character  of  the  participating  substances. 

Some  asymmetric  syntheses  of  this  type  have  been  effected, 
particularly  by  McKEXziE  and  his  coadjutors. 

Reduction  of  benzoylformic  acid,  CeHs-CO-COOH,  yields 
inactive  mandelic  acid,  CeHs.CHOH.COOH.  But  reduction  of 
an  ester  of  this  ketonic  acid  derived  from  an  optically  active 
alcohol,  such  as  the  laevo-rotatory  menthol,  produces  a  mixture  of 
the  ester  of  the  dextro-acid  with  a  small  excess  of  that  of  the 
Isevo-acid.  On  saponification,  active  mandelic  acid  is  obtained, 
despite  the  elimination  of  the  asymmetric  structure  occasioned  by 
the  menthol-residue.  The  formation  of  /-lactic  acid  by  the 
reduction  of  Z-bornyl  pyroracemate  with  aluminium-amalgam  is 
a  similar  reaction: 


/-Bornyl  pyroracemate  /-Lactic  acid 

Another  example  is  the  formation  of  excess  of  Z-tartaric  acid  by 
treating  monobornyl  fumarate  with  permanganate  (324). 

The  occurrence  in  nature  of  all  the  possible  optical  isomerides 
of  a  compound  is  exceptional.  Only  the  dextro-rotatory  forms  of 
dextrose,  tartaric  acid,  and  lactic  acid  are  natural  products.  Why 
nature  has  not  produced  the  chemical  mirror-images  of  all  optic- 
ally active  substances  found  in  the  existing  flora  and  fauna,  since, 
as  far  as  is  at  present  known,  the  probability  for  the  formation  of 
both  must  have  been  equal,  is  a  problem  by  no  means  solved. 

III.  POLYOSES. 
Raffinose,  CigH^OigjSH^O. 

224.  Raffinose  is  the  most  important  of  the  hexotrioses,  of  which 
but  few  are  known.     Their  formula  is  Ci8H32Oi6;  that  is, 

3C6H1206-2H.;O. 


290  ORGANIC  CHEMISTRY.  [§225 

Raffinose  is  a  hexotriose,  since,  on  hydrolysis,  it  takes  up  two 
molecules  of  water  with  formation  of  an  equal  number  of  molecules 
of  Isevulose,  dextrose,  and  d-galactose.  By  careful  hydrolysis,  raf- 
finose  can  be  split  up  quantitatively  into  Isevulose  and  a  diose  (mele- 
diose} :  from  the  latter,  dextrose  and  d-galactose  can  be  obtained  in 
the  same  way  as  from  lactose,  with  which,  however,  melediose  is  not 
identical.  The  action  of  emulsin  converts  raffinose  into  d-galactose 
and  sucrose.  Raffinose  exhibits  none  of  the  monose  reactions :  thus, 
it  does  not  reduce  an  alkaline  copper  solution.  This  proves  the 
absence  of  a  free  carbonyl-group,  so  that  raffinose  must  be  repre- 
sented by 

C6Hn05<O.C6H1004<0>C6HnO5. 

Melediose  exhibits  the  sugar  reactions,  and  therefore  contains  one 
free  carbonyl-group,  so  that  its  formula  is 

C6Hn06<O.C6Hn06<, 

which  proves  that  the  decomposition  of  raffinose  into  monose  and 
diose  takes  place  at  the  dicarbonyl-bond,  as  otherwise  there  would 
have  been  obtained  a  diose,  C6HnO5<O>C6HiiO6,  lacking  a  free 
carbonyl-group. 

Raffinose  crystallizes  with  five  molecules  of  water.  When  sucrose 
contains  a  certain  proportion  of  this  polyose,  it  yields  pointed 
crystals.  • 

M anneotetrose  is  a  tetrose  present  in  manna.  On  hydrolysis  it 
yields  two  molecules  of  galactose,  one  molecule  of  dextrose,  and  one 
molecule  of  Isevulose : 

C24H4202t+3H20  =  2C0HW06+C6H1,O.  +  C0HW08. 

Manneotetrose  Galactose        Dextrose       Lsevulose 


Higher  Polyoses. 

225.  Most  of  the  higher  polyoses  are  amorphous,  and  do  not 
possess  a  sweet  taste:  many  of  them  are  insoluble  in  water.  On 
hydrolysis,  they  yield  mohoses,  either  pentoses  or  hexoses,  so  that 
it  may  be  assumed  £hat  the  monose-residues  are  united  by  the 
oxygen  atom.  The  molecular  weight  of  the  polyoses  is  unknown, 
but  must  be  very  great.  Their  formula  may  be  represented  as 
being  derived  thus: 


§  225]  POLYOSES.  291 

If  n  is  very  great,  this  constitution  approximates  to 

nC6H1206-nH20=  n(C6H10O5); 

which  is  the  formula  indicated  by  the  results  of  analysis.  On 
hydrolysis,  nearly  all  the  polyses  yield  monoses  with  the  same 
number  of  C-atoms. 

Starch. 

Starch  is  the  first  observable  assimilation-product  of  plants. 
It  occurs  in  large  quantitites  in  the  tubers,  roots,  and  seeds  of  many 
plants,  in  which  it  is  present  in  the  form  of  granules  differing  in 
form  and  size  in  different  plants.  Some  of  these  granules  are 
represented  in  Figs.  67,  68,  and  69. 

Starch  is  insoluble  in  cold  water:  in  hot  water  it  swells  up 
without  dissolving.  It  yields  an  intense  blue  coloration  with  a 
dilute  solution  of  iodine,  for  which  this  reaction  serves  as  a  test. 

On  addition  of  a  concentrated  solution  of  tannin  under  the 
microscope  to  the  liquid  obtained  by  boiling  1  g.  of  potato-starch 
with  100  c.c.  of  water,  the  starch-granules  are  seen  to  consist  of  a 
skin,  filled  with  a  liquid  which  is  coagulated  by  the  action  of  the 
tannin.  Starch  is  therefore  built  up  from  two  distinct  individuals: 
the  skin,  called  amylocellulose;  and  the'soluble  part,  termed  granulose. 
Amylocellulose  constitutes  about  forty  per  cent,  by  weight  of  starch, 
and  can  be  prepared  from  it  by  extraction  of  the  granulose  with  a 
dilute  solution  of  sodium  hydroxide.  Only  the  granulose  produces 
the  blue  coloration  with  iodine. 

When  boiled  with  dilute  acids,  starch  is  converted  into  dex- 
trose. On  treatment  with  diastase,  starch-paste  first  liquefies, 
its  molecules  then  decompose,  and  ultimately  maltose  and  iso- 
maltose,  C^H^Oii,  are  formed.  Both  these  methods  of  treat- 
ment  yield  intermediate  products,  however;  they  are  gum-like 
substances,  polyoses  containing  a  smaller  number  of  atoms  in  the 
molecule  than  starch,  called  dextrins.  Dextrin  is  also  obtained 
by  heating  starch  alone,  or  to  110°  with  a  small  quantity  of  nitric 
acid. 

Starch  does  not  show  any  of  the  reactions  of  the  monoses:  it 


292 


ORGANIC  CHEMISTRY. 


[§225 


FIG.  67.— KYU-STARCH.     X  320. 


FIG.  63.— RICE-STARCH.     X  320. 


§225] 


POLYOSES. 


293 


does  not  reduce  an  alkaline  copper  solution,  nor  resinify  with  alka- 
lis, and  yields  no  compound  with  phenylhydrazine.     This  proves 


FIG.  69. — POTATO-STARCH.     X  250. 

the  absence  of  a  free  carbonyl-group,  so  that  its  molecule  must  be 
represented  by 

C6H10O5<O  . . . .  C6H10O4<0>C6H1004  ....  O>C6H10O5. 

It  might  be  suggested  that  the  molecule  of  starch  contains  more 
than  one  dicarbonyl-bond,  when  the  formula  would  be,  for  example, 

C6H1005<0  .  .  . '.  C6H1004<0>C6H1004.0>C6H1005  .  .  .  .  O> 
>C6H1004<0>C6H1004.0>C6H1005.0>C6H1005 O>C6H10O5. 

It  does  not,  since  hydrolysis  of  a  compound  of  this  type  must  yield, 
in  addition  to  dextrose,  a  substance  >C6Hi2O6<,  containing  two 
free  carbonyl-groups,  and  no  such  product  has  been  obtained  by  the 
hydrolysis  of  starch. 

Dextrin  can  unite  with  phenylhydrazine,  and  exhibits  the  reac- 
tions of  the  monoses,  such  as  reduction  of  an  alkaline  copper  solution, 
and  the  formation  of  a  yellow  coloration  with  alkalis.  It  must, 
therefore,  be  assumed  to  contain  a  free  carbonyl-group. 

Certain  dextrins  have  also  been  prepared  in  crystalline  form. 


294  ORGANIC  CHEMISTRY.  [§§  226,  227 


Glycogen,  (C6H10O5)X. 

Glycogen  is  a  substance  resembling  starch,  and  is  present  in  the 
animal  organism:  the  other  polyoses  are  vegetable  products.  It 
is  usually  prepared  from  liver,  and  is  a  white,  amorphous  powder, 
dissolving  in  water  with  formation  of  an  opalescent  solution.  On 
hydrolysis,  it  yields  only  dextrose.  Apparently  there  are  different 
kinds  of  glycogcn,  according  to  the  animal  from  which  it  is  isolated. 

Manufacture  of  Starch. 

226.  The  process  by  which  starch  is  manufactured  is  theoretically 
very  simple.  Potato-starch  is  prepared  by  first  finely  grinding  the 
potatoes,  whereby  the  cell-tissue  is  destroyed.  The  starch-granules, 
thus  laid  bare,  are  washed  out  of  the  cell-tissue  by  treatment  with 
water  in  a  specially  constructed  apparatus,  somewhat  resembling  a 
sieve.  They  are  allowed  to  settle  on  standing,  are  then  carefully 
washed,  and  finally  dried  slowly. 

Starch  is  employed  for  many  purposes  in  the  arts,  as  an  adhesive 
paste,  and  for  stiffening  linen  in  laundries.  In  the  latter  process,  the 
starch-paste  is  converted  by  the  heat  of  the  smoothing-iron  into  a 
stiff,  shining  layer  of  dextrin,  coating  the-  fibres  of  the  linen.  Starch 
is  of  great  importance  as  a  large  constituent  of  foods.  It  is  more 
fully  dealt  with  in  this  connexion  in  physiological  text-books. 

Cellulose,  (C6H1005)X. 

227.  Cellulose  is  a  polyose  of  very  high  molecular  weight.  The 
cell-walls  of  plants  consist  principally  of  this  substance,  together 
with  lignin,  which  is  probably  not  a  polyose. 

The  formula  of  lignin  is  unknown,  but  it  contains  the  groups 
methoxyl,  acetyl,  and  formyl.  The  formation  of  methyl  alcohol  by 
the  dry  distillation  of  wood  depends  on  the  presence  of  lignin,  since 
the  process  does  not  produce  this  alcohol  from  pure  cellulose.  A 
test  for  lignin  is  described  in  228. 

Cellulose  is  very  stable  towards  dilute  acids  and  alkalis,  a 
property  which  is  made  use  of  in  the  technical  preparation 
of  cellulose,  in  order  to  free  it  from  the  substances  present  along 
with  it  in  the  plant-material.  Linen,  cotton,  and  paper  consist 
almost  exclusively  of  cellulose:  pure  filter-paper  is  nearly  chem- 
ically pure  cellulose.  When  it  is  dissolved  in  strong  sulphuric 


§  228]  POLYOSES.  295 

acid,  and  the  solution  boiled,  after  dilution  with  water,  it  is 
completely  hydrolyzed.  Cellulose  from  cotton-wool,  paper,  etc., 
yields  exclusively  dextrose;  from  coffee-beans,  cocoa-nibs,  etc., 
d-mannose.  Cellulose  is  converted  by  treatment  with  sulphuric 
acid  containing  half  its  volume  of  water  into  a  colloidal  modifica- 
tion, amyloid,  which  gives  a  blue  coloration  with  iodine:  this 
reaction  furnishes  a  test  for  cellulose.  The  latter  is  soluble 
in  an  ammoniacal  solution  of  copper  oxide  (SCHWEITZER'S  reagent)  : 
from  this  solution  it  is  precipitated  chemically  unchanged  by 
acids  and  salts,  and  forms  an  amorphous  powder  when  dried. 

The  action  of  acetic  anhydride  and  concentrated  sulphuric 
acid  on  the  cellulose  of  filter-paper,  cotton-wool,  and  other  mate- 
rials, yields  the  octoacetyl-compound  of  a  diose,  ,named  cellose, 
obtained  by  saponification  of  the  acetyl-derivative  with  alcoholic 
potash.  Inversion  converts  cellose  into  dextrose.  It  is  the 
simplest  polyose  obtained  from  cellulose,  just  as  maltose  is  the 
simplest  polyose  formed  from  starch.  .  This  fact  furnishes  an 
important  argument  from  the  chemical  standpoint,  supported 
by  observations  in  vegetable  physiology,  in  favour  of  the  view 
that  cellulose  and  starch  are  essentially  different  substances, 
and  against  the  theory  that  cellulose  is  a  higher  polymeric  form 
of  starch. 

Technical  Applications  of  Cellulose;    Nitrocelluloses ;   Artificial 

Silk. 

228.  Linen  is  prepared  from  the  stalk  of  the  flax-plant.  The 
linen  fibres  can  be  obtained  from  the  flax,  cellulose  being  very 
stable  towards  chemical  reagents.  For  example,  the  flax  is  steeped 
in  water  for  from  ten  days  to  a  fortnight.  The  consequent  decay  of 
the  external  fibre  gives  rise  to  an  unpleasant  smell.  The  material  is 
then  dried  by  spreading  it  out,  and  passed  between  corrugated  rollers. 
This  loosens  the  external  woody  fibre,  which  is  then  stripped  off  by 
revolving  wooden  arms  named  " wipers,"  a  process  called  ''scutch- 
ing." The  linen-fibres  have  a  grey  colour,  and  are  bleached  by  either 
being  spread  out  in  the  open  or  by  means  of  blcaching-powder. 

Paper  was  formerly  prepared  almost  exclusively  from  linen-rags, 
but  is  now  largely  manufactured  from  wood  and  straw,  which  must 
be  divided  into  fibres;  the  fibres  arc  then  separated  as  much  as 
possible  from  the  other,  so-called  incrusting,  substances  present. 
This  is  effected  either  by  the  sulphite-method,  in  which  the  wood  is 


293  ORGANIC  CHEMISTRY.  [§  228 

heated  under  pressure  with  a  solution  of  calcium  hydrogen  sulphite; 
or  for  straw  by  heating  with  sodium  hydroxide  under  pressure.  By 
these  processes  most  of  the  incrusting  substances  are  dissolved,  and 
the  wood  or  straw  bleached  at  the  same  time  :  the  cellulose  which 
remains  can  be  readily  separated  into  fine  fibres,  which  is  necessary 
to  the  manufacture  of  pap^r-pulp.  It  is  not,  however,  possible  to 
remove  all  the  lignin  by  these  means;  in  consequence,  wood-paper 
and  straw-paper  answer  to  the  tests  for  lignin,  and  can  be  recognized 
thereby.  Lignin  gives  a  yellow  coloration  with  salts  of  aniline  (297), 
and  a  red  coloration  with  a  solution  of  phloroglucinol  (337)  in 
concentrated  hydrochloric  acid. 

Parchment-paper  is  prepared  by  converting  the  outer  surface  of 
paper  into  amyloid  (227),  a  process  which  imparts  toughness  to  it. 

The  nitrocelluloses  are  of  great  technical  importance.  When 
cotton-wool  is  treated  with  a  mixture  of  nitric  and  sulphuric  acids, 
a  mixture  of  mononitrocellulose,  dinitrocellulose  ,  and  tnnitrocellulose 
is  obtained,  the  extent  of  the  nitration  being  dependent  upon  the 
concentration  of  the  acids  and  the  duration  of  the  process.  Cellulose 
is  arbitrarily  assumed  to  have  the  molecular  formula  C6H1005.  In 
the  nitration  of  cellulose  the  final  product  is  trinitro-oxycellulose. 
For,  on  treatment  with  ferrous  chloride,  trinitro-oxycellulose  yields 
oxycellulose,  but  no  cellulose,  proving  that  the  formation  of  the 
trinitro-compound  is  accompanied  by  oxidation  of  the  cellulose; 
whereas  nitromannitol,  for  example,  is  reconverted  by  this  reagent 
into  mannitol,  without  oxidation  of  the  latter.  Oxycellulose  has  the 
formula 

(C24H40021)x    or    [(CGH1o0 


and  its  trinitro-derivative  is 

[C,H7(NOO,Oj3+CeH7(NO,).0.. 

The  solution  in  a  mixture  of  alcohol  and  ether  of  mononitrocellu- 
lose and  dinitrocellulose  is  known  as  collodion:  on  evaporation  it 
leaves  an  elastic  skin,  and  is  employed  in  photography,  and  in  the 
manufacture  of  celluloid.  The  trinitrocellulose  is  guncotton,  which 
looks  like  cotton-wool,  but  feels  somewhat  rough  to  the  touch,  and 
is  extensively  employed  as  an  explosive.  It  burns  readily  when  a 
loose  tuft  of  it  is  ignited,  but  can  be  made  to  explode  by  the  detona- 
tion of  a  small  quantity  of  mercury  fulminate,  and  yields  only 
gaseous  products,  nitrogen,  hydrogen,  water-vapour,  carbon  mon- 
oxide, and  carbon  dioxide.  It  exerts  a  detonating  or  brisant  (155) 
action,  and  without  modification  is,  therefore,  unsuitable  for  use  in 
artillery. 


§228]  NITROCELLULOSES.  297 

When  guncotton  is  dissolved  in  acetone  or  ethyl  acetate,  a  gelatin- 
ous mass  is  obtained:  after  removal  of  the  solvent,  an  amorphous, 
transparent  substance  is  left,  having  the  same  chemical  composition 
as  guncotton,  but  burning  and  exploding  more  slowly.  The  velocity 
of  explosion  of  guncotton  being  thus  moderated,  it  is  made  available 
in  this  form  for  use  in  artillery,  under  the  name  of  "  smokeless 
powder." 

Artificial  silk  is  manufactured  by  forcing  a  solution  of  cellulose 
through  very  narrow  orifices  immersed  in  a  bath  which  repre- 
cipitates  the  cellulose  in  lustrous  threads  resembling  silk  in  appear- 
ance. Photographic  film  is  made  similarly,  the  orifices  being 
replaced  by  a  narrow  slot. 

On  the  manufacturing  scale  the  cellulose  is  brought  into  solution 
by  one  of  three  processes:  (1)  by  means  of  SCHWEITZER'S  reagent 
(227);  (2)  by  preliminary  nitration  to  mononitrocellulose  and 
dinitrocellulose,  and  solution  of  these  nitro-compounds  in  alcohol 
and  ether,  the  threads  being  then  denitrified  by  the  action  of 
various  reducers;  (3)  by  conversion  of  the  cellulose  into  a  xanthate 
(264),  a  very  thick  liquid  being  formed,  the  so-called  viscose. 
To  coagulate  the  fibres,  the  solution  obtained  by  the  first  method 
is  pressed  out  into  dilute  acid;  that  produced  by  the  second  method 
into  a  large  amount  of  water;  and  that  formed  by  the  third  method 
into  a  solution  of  ammonium  sulphate  or  dilute  sulphuric  acid. 


AMINO-ALDEHYDES  AND  AMINO-KETONES. 
229.    Very  few  amino-aldehydes  and  amino-ketones  are  known. 

T_T 

Aminoacetaldehyde,  CH2NH,'CQ,  a  very  unstable  compound,  can  be 

TT 

obtained  from  ammoacctal,  CILNHv'C,™-,  u  \  ,  which  can  be  pre- 


pared  from  monochloroacetal,  £tL'Cl  'CHKKkH^.    Muscarine  is 
possibly  the  corresponding  trimethylammonium  base: 

CH2N(CHa)aOH 


It  is  a  crystalline,  excessively  poisonous  substance,  and  is  present  in 
certain  plants  —  for  example,  toad-stool  (Agancus  muscarius). 

Apart  from  inorganic  substances,  chitin  is  the  principal  con- 
stituent of  the  shells  of  the  Crustacea,  and  is  best  prepared  from 
the  shell  and  claws  of  the  lobster.  When  boiled  with  concentrated 
hydrochloric  acid,  chitin  is  almost  wholly  converted  into  gluco- 
samine hydrochloride,  C6Hi3O5N,HCl,  a  well-crystallized  salt. 
Chitin  contains  an  NH2-group,  since  like  primary  amines  it 
evolves  nitrogen  on  treatment  with  nitrous  acid,  yielding  chitose, 
C6H12O6,  with  the  properties  of  an  aldose.  Thus,  it  is  oxidized  by 
bromine-water  to  the  monobasic  chitonic  acid:  further  oxidation 
with  nitric  acid  converts  this  substance  into  the  dibasic  isosaccharic 
acid. 

Bromine  converts  glucosamine  hydrochloride  into  d-glucosamic 
acid,  CH2OH.(CHOH)3.CHNH2-COOH,  which  EMIL  FISCHER  has 
synthesized  by  the  following  method.  Ammonia  and  hydrocyanic 
acid  react  with  d-arabinose  to  form  a  compound  (240,  3), 

CH2OH  •  (CHOH)3  •  CHNH2  •  CN, 
and  with  concentrated  hydrochloric  acid  this  yields 
CH2OH  •  (CHOH)3  •  CHNH2  -  COOH, 

identical  with  glucosamic  acid.  Since  this  acid  is  reduced  to 
glucosamine  by  the  method  of  206,  5,  the  identity  of  the 
synthetic  amine  with  the  natural  product  is  established. 

298 


ALDEHYDO-ACIDS  AND  KETONIC  ACIDS. 


Glyoxylic  Acid, 

230.  Glyoxylic  acid  is  the  first  member  of  the  series  of  aldehydo- 
acids.  It  is  present  in  unripe  fruits,  and  can  be  prepared  by  heat- 
ing dibromoacetic  acid,  CHBr2«COOH,  with  water,  or  by  the 
electro-reduction  of  oxalic  acid.  It  also  results  on  the  oxidation 
of  alcohol  with  nitric  acid,  by  the  method  described  under  glyoxal 
(198). 

As  the  above  formula  shows,  glyoxylic  acid  contains  one  mole- 
cule of  water,  which  cannot  be  separated  from  the  acid  or  its  salts 
without  their  undergoing  decomposition.  For  this  reason,  the 
water  is  often  assumed  to  be  in  chemical  combination  (149) ;  thus, 
CH(OH)2«COOH,  as  it  is  in  chloral  hydrate  (201).  In  each  of 

TT 

these  substances  the  aldehydo-group,  — CQ,  is  under  the  influence 

of  a  strongly  negative  group;  — CC13  in  chloral,  and  — COOH  in 
glyoxylic  acid.  The  latter,  moreover,  possesses  all  the  properties 
characteristic  of  aldehydes:  it  reduces  an  ammoniacal  silver  solu- 
tion, forms  an  addition-product  with  sodium  hydrogen  sulphite, 
yields  an  oxime,  etc.  When  boiled  with  caustic  potash,  it  is  con- 
verted into  glycollic  acid  and  oxalic  acid,  the  formation  of  which 
may  be  explained  by  the  assumption  that  one  molecule  of  the  acid 
takes  up  the  two  hydrogen  atoms,  and  another  the  oxygen  atom, 
from  one  molecule  of  water: 

2COOH.CHO  =  COOH.  CH2OH+ COOH.  COOH. 

299 


300  ORGANIC  CHEMISTRY.  [§231 

Pyroracemic  Acid,  CHg-CO-COOH. 

23  1  .  Pyroracemic  (pyruvic)  acid,  the  first  member  of  the  series  of 
ketonic  acids,  owes  its  name  to  its  formation  by  the  distillation  of 
either  tartaric  acid  or  racemic  acid  with  potassium  hydrogen  sulphate. 
It  is  probable  that  carbon  dioxide  is  first  eliminated  from  tar- 
taric  acid,  COOH  .  CHOH  .  CHOH  .  COOH,  withf  ormation  of  gly  eerie 
acid,  CH2OH'CHOH-COOH,  which  yields  pyroracemic  acid  by 
loss  of  one  molecule  of  water;  for  glyceric  acid  itself  is  con- 
verted into  pyroracemic  acid  by  heating  with  potassium  hydrogen 
sulphate: 

CH2OH.  CHOH.  COOH  -H20  = 

=  CH2=C(OH)  -COOH  -*  CH3  -CO-  COOH. 

Pyroracemic  acid  can  be  obtained  synthetically  by  hydrolysis  of  the 
oitrile  formed  by  the  action  of  potassium  cyanide  on  acetyl  chloride: 

CH3  -  COC1  ->  CH3  -  CO  -  CN  ->  CH3  .  CO  •  CO2H. 

This  is  a  general  method  for  the  preparation  of  a-ketonic  acids. 

When  heated  to  ISO"  with  dilute  sulphuric  acid,  pyroracemic 
acid  yields  carbon  dioxide  and  acetaldehyde: 


+CO2. 

At  ordinary  temperatures  pyroracemic  acid  is  liquid,  but  is  solid 
at  low  temperatures.  It  melts  at  9°,  boils  at  165°,  and  is  miscible 
with  water  in  all  proportions:  its  specific  gravity  is  1-27  at  20°, 
and  it  has  an  odour  resembling  that  of  acetic  acid.  It  is  a  stronger 
acid  than  propionic  acid,  for  which  1G4&  is  0'134;  for  pyroracemic 
acid  104fc  is  56,  which  must  be  explained  by  assuming  the  presence 
of  a  negative  carbon  yl-group  in  juxtaposition  to  the  carboxyl-group. 

Pyroracemic  acid  has  all  the  properties  characteristic  of  ketones: 
it  yields  an  oxime,  a  hydrazone,  an  addition-product  with  hydro- 
cyanic acid,  etc. 

On  boiling  with  a  solution  of  barium  hydroxide,  pyroracemic 
acid  is  readily  converted  into  a  condensation-product,  uvitic  or 
symmetrical  methylisophthalic  acid  (350),  a  reaction  analogous  to  the 
formation  of  mcsitylene  from  acetone  (285). 

The  electrolysis  of  a  very  concentrated  solution  of  potassium 
pyroracemate  yields  acatic  acid  and  diacetyl.  The  formation  of 


§232]  ACETO  ACETIC  ACID..  301 

acetic  acid  may  be  looked  upon  as  due  to  the  interaction  of  the  anion 
of  the  acid  and  the  hydroxyl-ion,  after  discharge  at  the  anode  : 

CH3-CO-COO'+OH'  =  CH3-COOH+CO2; 

and  that  of  diacetyl  as  resulting  from  the  union  of  two  acid  anions, 
with  elimination  of  CO2  : 

CH3.CO.CO.CH3+2C02. 

The  potassium  salts  of  other  ketonic   acids   are    decomposed   by 
electrolysis  in  an  analogous  manner. 

Acetoacetic  Acid,    CH3.CO.CH2-COOH. 

232.  Acetoacetic  acid  is  a  /?-ketonic  acid.  It  is  not  of  much 
importance,  but  its  ester,  ethyl  acetoacetate,  CH3  •  CO  •  CH2  •  COOC2H5, 
is  an  interesting  compound. 

Ethyl  acetoacetate  is  obtained  by  CLAISEN'S  condensation- 
method  (200)  through  the  action  of  sodium  on  ethyl  acetate  in 
presence  of  ethyl  alcohol: 

ONa       H 


Ethyl  acetate  ddition-product 

.ONa 
=  2C2H5OH  +  CH3  •  C=CH  -  COOC2H5. 

Ethyl  sodioacetoacetate 

The  foregoing  explanation  of  the  condensation  was  proved  to  be 
correct  in  this  instance  by  CLAISEN,  who  found  that  ethyl  aceto- 
acetate cannot  be  prepared  by  the  action  of  sodium  on  ethyl 
acetate  which  has  been  carefully  purified  from  alcohol.  The  free 
ester,  CH3«CO-CH2-COOC2H5,  can  be  obtained  by  treatment 
of  the  sodium  compound  with  acetic  acid,  since  in  the  substitu- 
tion of  sodium  by  hydrogen  the  group  —  C(OH):CH  —  •  is  first 
formed,  and  subsequently  transposed  into  —  CO«CH2  —  (131). 

Ethyl  acetoacetate  is  a  colourless  liquid,  slightly  soluble  in 
water,  and  characterized  by  an  agreeable  odour:  it  boils  at  1S19, 
and  has  a  specific  gravity  of  1-030  at  15°.  It  can  be  hydrolyzed 
in  two  ways,  respectively  known  as  the  ketone  decomposition 
•{weak  hydrolysis)  and  the  acid  decomposition  (strong  hydrolysis}, 
on  account  of  the  nature  of  the  products. 

The  ketone  decomposition  is  effected  by  heating  ethyl  aceto- 


302 


ORGANIC  CHEMISTRY. 


(§232 


acetate  with  dilute  sulphuric  acid,  or  with  a  dilute  aqueous  solution 
of  alkali,  the  products  being  acetone,  carbon  dioxide,  and  alcohol: 


CH3.CO-CH2. 
+  H 


CO, 


The  acid  decomposition  takes  place  when  ethyl  acetoacetate  is 
heated  with  a  very  concentrated  solution  of  alcoholic  potash  or  soda : 


CH3-CO 
+  OH 


CH2-COO 
H  +  H 


CoH, 


=  CH3  -  COOH  +  CH3  •  COOH  +  C2H5OH, 


The  great  importance  of  ethyl  acetoacetate  for  syntheses  arises 
from  its  capability  of  undergoing  these  two  decompositions, 
together  with  the  existence  of  a  great  many  derivatives  with  one 
or  two  of  the  hydrogen  atoms  of  the  CH2-group  replaced  by 
substituents.  Replacement  of  one  or  two  hydrogen  atoms  by 
one  or  two  groups  R  gives  the  compound 

CH3.CO-CHR.COOC2H5    or    CH3.CO-CR2.COOC2H5, 

converted   respectively  by  the  ketone   decomposition  into  the 
ketone  • 

CH3.CO-CH2R    or    CH3.CO-CHR2, 

a  reaction  affording  a  general  method  of  synthesizing   methyl- 
ketones  (101). 

The  acid  decomposition  converts  the  compounds 

CH3.CO.CHR.COOC2H5   and   CH3.CO.CR2.COOC2H5 
into  acetic  acid  and  an  acid  with  either  the  formula 
CH2R-COOH    or    CHR2-COOH; 

.the  reaction  furnishing  a  general  method  for  the  synthesis  of 
monobasic  acids. 

The  mechanism  of  the  formation  of  such  derivatives  of  ethyl 
acetoacetate  involves  interaction  of  sodium  ethoxide  and  the  ester 
to  form  a  sodium  compound,  CH3-C(ONa)  :CH-COOC2H5  (235). 


§233]  ACETOACETIC-ESTER  SYNTHESIS.  303 

Addition  of  an  organic  halide,  R-X;  in  which  X  represents  a 
halogen  atom,  gives  the  product 

ONa   H 

CH3-C  --  C.COOC2H5. 
X        R 

Elimination  of  NaX  from  this  substance  yields  the  compound 
CH3-CO-CHR.COOC2H5,  the  hydrogen  atom  of  its  CHR-group 
being  capable  of  analogous  replacement. 

233.  A  few  examples  of  this  synthetical  method  are  appended. 

1.  Methylnonylketone,  the  principal  constituent  of  oil  of  rue 
(from  Ruta  grareolens)  ,  can  be  obtained  by  the  action  of  n-octyl 
iodide  upon  ethyl  sodioacetoacetate  : 

CH3  •  C  (ONa)  :  CH  i  COOC2H6  CH3  •  CO  •  CH  •  COOC2H6 

+  -»  | 

I  —  CsHn  CsHn 

It  yields,  by  the  ketone  decomposition,  methylnonylketone, 
CH,-CO-CH2«C8Hi7. 

Ethyl  n-octylacetoacetate  yields,  by  the  acid  decomposition,  capric 
acid,  CioH2002,  which  must  therefore  have  a  normal  carbon  chain 


2.  Heptylic  acid,  which  is  obtainable  from  Isevulose  by  the  cyano- 
hydrin-synthesis  (209),  can  be  synthetically  built  up  from  ethyl 
acetoacetate  by  the  successive  introduction  of  a  methyl-group  and  a 
n-butyl-group  :  this  proves  it  to  be  methyl-n-butylacetic  add: 

CH,-C(ONa)  :CH-COOC2H5  /COOC2H6 

+  -*    CH3-CO-CH<(  -, 

J.       v^4Jlg  v>4il9 

Ethyl  n-butylacetoacetate 

CH3-C(ONa)  :C  < 
.-»  + 

I—  CH3  CH3 

Ethyl  methyl-n-butylacetoacetate 

Ethyl  methyl-n-butylacetoacetate  yields,  by  the  acid  decomposition, 
methyl-n-butylacetic  acid, 

COOH 


49    . 
XCH3 


304  ORGANIC  CHEMISTRY  [§  234 

3.  Y-Ketonic  acids  are  obtained  by  the  action  of  ethyl  acetoace- 
tate   upon   the    esters    of   the    a-halogen-substituted   fatty    acids, 
followed  by  the  ketone  decomposition  :j 

CH3  •  C(ONa) :  CH  •  COOCZH5  /COOC2H6 

+  -»  CH.-CO-CH/ 

x — CHR  •  cooc2H6  NCHR  •  cooc2H6 

This  yields,  by  the  ketone  decomposition, 

CH3  •  CO  •  CH2  •  CHR  •  COOH. 
T       P        « 

4.  When  iodine  acts  upon  ethyl  sodioacetoacetate,  two  molecules 
unite  thus: 

CH3-C(ONa)  :CH-COOC2H6       CH;).Q/ !CH-COOC2H6 

21 


CH3-C(ONa):CH-COOC2H5       CH3-C^— CH-COOC2H5 

Elimination  of  two  molecules  of  sodium  iodide  converts  this  com- 
pound into  diethyl  diacetylsuccinate, 

CH3  •  CO  •  CH CH  •  CO  •  CH3 

I  I 

COOC2H6     COOC2H6 

When  boiled  with  a  20  per  cent,  solution  of  potassium  carbonate, 
diethyl  diacetylsuccinate  loses  carbon  dioxide  and  alcohol,  with 
formation  of  acetonylacetone  (200) : 


CH3  •  CO  •  CH— CH  •  CO  •  CH3 

|H     |H 


|O2C       |C02  C2H6 
OH 


CH3  •  CO  •  CH2  •  CH2  •  CO  •  CH3. 

Acetonylacetone 


Lsevulic  Acid,  CH3-CO-CH2.CH2.COOH. 

234.  Lcevulic  acid  is  the  simplest  f-ketonic  acid:  it  can  be 
obtained  by  the  synthetical  method  described  in  233,  3 — from 
ethyl  acetoacetate  by  the  action  of  ethyl  monochloroacetate;  in 
this  instance,  in  the  formula  given  R=H.  When  hexoses  are 


§235]  MESOXALIC  ACID.  305 

boiled  with  concentrated  hydrochloric  acid,  laevulic  acid  is  pro- 
duced (211):  it  is  usually  prepared  by  this  method,  which  has 
not  yet  been  fully  explained. 

Lsevulic  acid  is  crystalline:  it  melts  at  33*5°,  and  boils  with 
slight  decomposition  at  250°.  It  yields  an  oxime  and  a  hydrazone, 
and  an  addition-product  with  hydrocyanic  acid:  in  short,  it 
exhibits  all  the  reactions  characteristic  of  ketones. 

Mesoxalic  Acid,  C3H2O5,H2O. 

Mesoxalic  acid  is  a  type  of  the  dibasic  ketonic  acids.  Its 
constitution  is  proved  by  the  formation  of  ethyl  mesoxalate  when 
diethyl  dibromomalonate,  Br2C(COOC2H5)2,  is  boiled  with  baryta- 
water: 


(C2H5OOC)  2C|Br2  +  BaJ  (OH)  2  =  (C2H5OOC)  2C  (OH)  2  +  BaBr2. 

Mesoxalic  acid  is  an  important  decomposition-product  of  uric 
acid.  Like  glyoxylic  acid  (230),  it  can  only  be  obtained  with  one 
molecule  of  water.  An  ester  of  the  anhydrous  acid  is,  however, 
known:  it  very  readily  adds  on  water.  The  constitution 
(COOH)2C(OH)2  must  therefore  be  assigned  to  the  free  acid  (149) 
which  has  most  of  the  properties  of  ketones,  just  as  chloral  hydrate 
(201)  and  glyoxylic  acid  show  most  of  the  reactions  of  aldehydes. 
When  boiled  with  water,  mesoxalic  acid  loses  carbon  dioxide, 
forming  glyoxylic  acid : 

CO^H.C(OH)2'COOH. 

It  is  not  surprising  that  a  compound  containing  a  carbon  atom 
loaded  with  four  negative  groups  should  break  down  thus.  The 
decomposition  takes  place  more  readily  than  that  of  malonic  acid, 
which  does  not  lose  carbon  dioxide  till  heated  above  its  melting- 
point,  to  140°- 150°. 

TAUTOMERISM. 

235.  The  conversion  of  ethyl  acetoacetate  into  its  sodium 
derivative,  and  the  interaction  of  this  substance  with  an  alkyl 
iodide,  yield  derivatives  in  which  the  alkyl-group  introduced 
is  undoubtedly  attached  to  a  carbon  atom  (232).  Sometimes 
the  reaction  proceeds  differently,  the  metallic  atom  of  the  sodium 
derivative  being  replaced  by  a  substituent  which  becomes  linked 


306  ORGANIC  CHEMISTRY.  [§  235 

to  the  molecule  through  oxygen.  An  example  is  furnished  by 
the  interaction  of  ethyl  sodiocetoacetate  and  ethyl  chloroformate 
(263),  two  compounds  being  formed.  The  one  produced  in 
smaller  proportion  is  the  C-derivative : 

ONa  ONa 

CH3.C:CH.COOC2H5    ->    CH3-C — CH.COOC2H5  = 

C1.COOC2H5  Cl     COOC2H5 

COOC2H5 

=C^3-CO.CH  +NaCl. 

COOC2H5 

The  identity  of  this  product  with  that  formed  by  the  interaction 
of  acetyl  chloride  and  diethyl  sodiomalonate  proves  its  con- 
stitution : 

CH3 •  COjCITNal •  CH (COOC2H5) 2  -»  CH3-CO.CH(COOC2H5)2. 
The  main  product  is  an  isomeride,  the  O-derivative : 

CH3  •  C (ONa) :  CH  •  COOC2H5     CH3  •  C :  CH  •  COOC2H5 

+  +NaCl. 

Cl— COOC2H5  O  •  COOC2H5 

The  presence  of  a  double  carbon  bond  in  the  molecule  is 
proved  by  the  instantaneous  formation  of  an  addition-product 
with  bromine. 

The  mechanism  of  the  interaction  of  ethyl  chlorocarbonate 
and  sodioacetylacetone  is  exactly  analogous,  the  C-derivative 
being  produced  in  small  proportion: 

CH3-C(ONa):CH.CO-CH3  CHg-CO-CH-CO-CHg 

+  ->  I 

Cl—  COOC2H5  COOC2  H5 

The  constitution  of  this  compound  follows  from  its  ready  decom- 
position into  potassium  acetate  and  ethyl  acetoacetate  by  heating 
with  an  equimolecular  proportion  of  potassium  hydroxide: 


H 
CH3-CO-CH 


OK 

CO  •  CH3  =  CH3  •  CO  •  CH2  •  COOC2H5  +  CH3  •  COOK. 


COOC2H5 


Ethyl  acetoacetate  Potassium 

acetate 


§235]  TAUTOMERISM.  307 

The  O-derivative,  however,  is  the  principal  product : 

CH3.C(ONa):CH.CO-CH3     CH3.C:CH.CO.CH3 

+  +NaCL 

Cl— COOC2H5  O  •  COOC2H5 

Its  formula  is  proved  by  the  ready  formation  of  an  addition- 
product  with  bromine,  and  its  decomposition  into  acetylacetone, 
ethyl  alcohol,  and  carbon  dioxide  by  dilute  alkalis  at  ordinary 
temperature : 


CH3.C:CH.CO-CH3 


A. 


|CQ2C2H5 


OH 


=CH3.C(OH):CH.CO.CH3 


•  Acetylacetone 


The  interaction  of  ethyl  acetoacetate  and  acid  chlorides  can 
be  completely  controlled  so  as  to  produce  either  a  C-derivative  or 
an  0-derivative.  If  the  usual  method  is  employed,  ethyl  sodio- 
acetoacetate  being  first  prepared,  and  then  brought  into  con- 
tact with  the  acid  chloride,  a  C-derivative  is  produced.  But  slow 
addition  of  the  acid  chloride  to  a  solution  of  ethyl  acetoacetate 
in  pyridine  (387)  results  in  the  exclusive  formation  of  the  0- 
derivative : 


CH3  •  CO  •  CH  -  COOC2H5  CH3  •  C^CH  -  COOC2H5 

;  I 

>CH3  O-Cq-CH3 

C-derivative  O-deriyative 

(Gives  no  addition-product  (Gives  an  addition-product 

with  bromine)  with  bromine) 


CO 


Similar  equivocal  reactions  have  been  observed  for  many 
compounds  with  the  grouping  — CO  •  CH2  •  CO — .  It  was  formerly 
believed  that  the  production  of  a  C-derivative  was  occasioned  by 
direct  linkage  of  the  sodium  atom  to  carbon,  — CO-CHNa-CO— , 
and  that  of  the  O-derivative  by  direct  union  of  the  sodium  atom 
with  oxygen,  — C(ONa):GH'CO — .  It  was  accordingly  assumed 
that  in  compounds  of  this  type  there  was  continual  alternation 
between  the  groupings  —  CO»CH2«CO —  and  — C(OH)  :CH-CO— . 
The  phenomenon  received  the  name  tautomerism  or  desmotropy. 


308  ORGANIC  CHEMISTRY.  ['§  236 

Although  later  investigation  proved  the  metallic  atom  in  the 
sodium  compounds  to  be  in  union  with  oxygen,  as  will  be  shown 
subsequently,  it  has  also  demonstrated  the  liquid  derivatives,, 
such  as  ethyl  acetoacetate,  to  be  a  mixture  of  two  isomerides  of 
the  type  indicated,  each  being  very  readily  transformed  into  the 
isomeric  compound.  This  view  is  based  on  direct  isolation  of  the 
tautomeric  forms. 

Ethyl  acetoacetate  is  the  classic  example  of  a  tautomeric 
substance.  By  cooling  it  to  a  low  temperature,  KNORR  isolated 
the  ketonic  form,  CHs-CO'CH^'COCX^Hs,  in  crystals  melting 
at  —39°.  By  the  action  of  an  equivalent  quantity  of  anhydrous 
hydrogen  chloride  on  a  suspension  of  ethyl  sodioacetoacetate 
in  strongly  cooled  light  petroleum,  followed  by  filtra- 
tion of  the  sodium  chloride  and  evaporation  of  the  solvent 
at  a  low  temperature,  KNORR  isolated  the  enolic  form 
CH3-C(OH):CH-COOC2H5,  a  substance  requiring  for  solidifica- 
tion the  refrigerating  action  of  liquid  air.  This  separation  proves 
the  sodium  derivative  to  have  the  enolic  structure. 

236.  The  ketonic  form  and  the  enolic  form  of  a  tautomeric 
substance  admit  of  ready  identification  by  both  physical  and 
chemical  means.  The  most  important  physical  method  is 
furnished  by  refraction,  the  presence  of  a  double  carbon  bond  in 
the  enolic  form,  and  its  absence  in  the  ketonic  form,  making  the 
refraction  of  the  enolic  compound  higher  than  that  of  the  ketonic 
compound  (120).  By  the  aid  of  this  physical  property,  the 
proportion  of  the  two  isomerides  present  in  a  liquid  mixture  can 
be  determined,  provided  the  refraction  of  each  component  in 
the  pure  state  is  known. 

Two  main  chemical  methods  of  distinguishing  the  two  forms 
are  available: 

1.  Addition  of  a  small  proportion  of  ferric  chloride  to  a  dilute 
aqueous  or  alcoholic  solution  of  an  enolic  compound  produces  a  deep 
coloration,  usually  violet ;  but  ketonic  derivatives  remain  colourless. 

2.  The  action  of  bromine  in  alcoholic  solution,  K.  H.  MEYER 
having  discovered  that  in  this  solution  enolic  compounds  form 
addition-products  with  bromine  instantaneously,  but  that  ketonic 
compounds  do  not.     The  method  has  been  applied  by  him  to 
determine  the  proportion  of  the  enolic  form  present  in  a  tauto- 
meric mixture. 


§236] 


TAUTOMERISM. 


309 


These  aids  can  be  applied  to  the  elucidation  of  the  conditions 
governing  the  ketonization  of  an  enolic  compound,  and  the  inverse 
enolization  of  a  ketonic  compound.  The  nature  of  the  solvent 
is  of  primary  importance.  For  ethyl  acetoacetate  in  the  liquid 
state  the  equilibrium  between  the  two  forms  corresponds  with  a 
small  percentage  of  the  enolic  derivative,  and  about  90  per  cent, 
of  the  ketonic  form.  The  subjoined  table  indicates  the  percentage 
of  the  enolic  form  of  ethyl  acetoacetate  in  various  solvents  at 
18°,  the  amounts  being  determined  by  titration  with  bromine. 


Solvent. 

Percentage  of 
Enolic  Form. 

Solvent. 

Percentage  of 
Enolic  Form. 

1V1  ethyl  alcohol 

6-9 

Methyl  alcohol  (50  per 

Ethyl  alcohol 

12-0 

cent.)  

1.5 

Amyl  alcohol 

15-3 

Ether 

27.1 

Water  

0-4 

Carbon  disulphide  

32-4 

Hexane 

46  «4 

For  ethyl  acetoacetate  itself  the  temperature  has  little  influence 
on  the  equilibrium,  but  the  freshly  distilled  product  contains 
about  20-25  per  cent,  of  the  enolic  form,  which  becomes  trans- 
formed slowly  into  the  ketonic  modification.  In  other  instances, 
rise  of  temperature  has  been  proved  to  cause  displacement  of  the 
equilibrium  towards  the  enolic  side,  although  usually  not  to  any 
great  extent. 

The  velocity  of  translation  of  each  form  can  be  determined 
by  starting  with  the  pure  modifications,  and  noting  the  proportion 
of  each  component  present  after  the  lapse  of  known  intervals  of 
time.  The  velocity-constant  of  the  ketonization  of  ethyl  aceto- 
acetate has  been  proved  to  be  much  greater  than  that  of  the  enoli- 
zation. Different  tautomeric  compounds  generally  exhibit  wide 
divergence  in  the  velocity  of  transformation  in  either  direction. 

A  qualitative  demonstration  of  the  transformation  of  the  enolic 
form  of  ethyl  acetoacetate  into  the  ketonic  modification  can  be 
made  by  adding  an  equivalent  amount  of  hydrochloric  acid  to  a 
dilute  aqueous  solution  of  ethyl  sodioacetoacetate.  The  enolic  form 
separates  in  fine  drops,  its  solubility  in  water  at  0°  being  about 
0-5  per  cent.  Owing  to  transformation  of  the  enolic  form  into  the 
ketonic  modification,  the  drops  gradually  dissolve,  the  solubility  of 
the  ketonic  derivative  in  water  at  0°  being  about  11  per  cent. 


310  ORGANIC  CHEMISTRY.  [§  237 

Enolic  compounds  dissolve  instantly  in  caustic  alkali;  but 
ketonic  compounds  do  not,  their  solution  proceeding  slowly  as 
they  change  to  the  enolic  form.  On  subsequent  addition  of  acid, 
the  enolic  modification  is  first  obtained,  but  not  the  ketonic 
component. 

Tautomerism  of  Oximes. 

237.  The  structural  formula,  -^/>  C=NOH,  has  been  assigned 

to  the  oximes  (103).     The  action  of  hydroxylamine  on  aldehydes 
and  ketones  admits  of  another  explanation,  indicated  in  the  scheme : 

HO.  ,0 

>CO+       >NH=H20  +  >C<|     • 
W  XNH 

Experiments  directed  to  proving  which  of  these  formulae  is 
right,  have  shown  that  the  oximes  are  tautomeric  in  the  sense  of 
the  scheme 


=NOH  <=±  >C<  J 

H 


The  following  exemplifies  the  method.  When  acetoxime  is  treated 
with  methyl  iodide,  the  methyl-group  becomes  linked  to  nitrogen, 
as  is  proved  by  reduction  of  the  resulting  compound  to  methyl- 
amine  and  acetone : 

/O 

(CH3)2C<;  +2H  =  (CHS)2CO  +  NH2.CH3. 

\N-CH3 

But  when  sodium  methoxide  is  added  to  a  mixture  of  methyl  iodide 
and  the  oxime — whereby  the  sodium  derivative  of  the  ketoxime  is 
first  formed — there  results  an  isomeric  substance  convertible  by 
hydrochloric  acid  into  acetone  and  a  compound,  NH2  •  OCH3.  Heat- 
ing with  hydriodic  acid  transforms  this  body  into  hydroxylamine 
and  methyl  iodide,  proving  that  its  methyl-group  is  linked  to  oxygen. 


§238]  PYRONE  DERIVATIVES.  311 

PYRONE  DERIVATIVES. 
238.  A  number  of  compounds  assumed  to  contain  the  group 

CO 
HC/^CH 


HC,      ,CH 


O 

are  known:    they  are  called  pyrone  derivatives,  and  some  of  them 
occur  naturally. 

Chelidonic  acid,  CyH^Oe,  so  called  because  it  is  found  in 
Chclidonium  majus  (greater  celandine),  forms  colourless  salts, 
C7H2O6M2:  it  also  yields  yellow  salts,  CyH^OyM^  which  are  de- 
rived from  an  acid  CyHeOy,  xanthochelidonic  acid.  When  set  free 
from  its  salts,  this  acid  readily  loses  one  molecule  of  water,  and  is 
reconverted  into  chelidonic  acid.  By  boiling  with  alkalis,  the  lat- 
ter is  decomposed  almost  quantitatively  into  two  molecules  of  oxalic 
acid  and  one  molecule  of  acetone: 

C7H406+3H20  =  2C2H204+C3H60. 

Oxalic  acid         Acetone 

These  properties  are  expressed  by  the  structural  formula 
i 

CO 


II        II 
HOOC-a      /C-COOH 


O 

Chelidonic  acid 

and  consequently  the  acid  can  be  called  pyronedicarboxylic  acid. 
Xanthoohelidonic  acid  must  then  have  the  structural  formula 

PTr  P  /COOH 
/U       <OH 
CO 


COOH 


312  ORGANIC   CHEMISTRY.  [§239 

in  which  the  two  hydroxyl-hydrogen  atoms  are  also  replaceable  by 
metals;  or,  in  its  tautomeric  form, 

/CH2—  CO-  COOH 
CO 
\CH2—  CO-COOH 

The  manner  in  which  it  is  decomposed  by  water  is  evident  from 
the  equation 

H2    O 
xCH  :  C—  COOH  JW.     C—  COOH 

CO         \0  +3H20  =  CO       +  y$* 

\3H  :  C—  COOH  \CH     C—  COOH 

Chelidonic  acid  JJ        Q 

Moreover,  a  synthesis  of  chelidonic  acid  corroborates  this  for- 
mula. The  starting-point  is  acetone,  which  by  CLAISEN'S  method 
(200  and  232)  can  be  condensed  with  two  molecules  of  diethyl 
oxalate: 


.CHg     C2H5OOC.COOC2H5 
CO        +  =CO  +2C2H6OH. 

C2H5OOC  -  COOC2H5      \3H  :  C  < 


The  product  is  an  ester  of  xanthochelidonic  acid.  When  this  is 
heated  with  concentrated  hydrochloric  acid,  two  objects  are  simul- 
taneously attained  —  the  ester  is  saponified,  and  one  molecule  of 
water  eliminated.  These  reactions  yield  a  compound  with  the 
structural  formula  given  above  for  chelidonic  acid,  and  identical 
with  it. 
<  239.  An  important  pyrone  derivative  is  dimethylpyrone: 

/CH=C.CH3 
CO  \O    . 


It  can  be  synthesized  from  ethyl  copper-acetoacetate  and  carbonyl 
chloride  (263)  : 


§  239]  PYRONE  DERIVATIVES.  313 

CH3.CO          CO-CHs  CH3.CO  CO-CHg 

II  II 

HC— Cu— CH  =CuCl2+     HCX         /CH 

/\CO/\ 

C2H5OOC   +  C12        COOC2H5        C2H5OOC  COOC2H5 

CO 

On  saponification  with  dilute  sulphuric  acid,  two  molecules  of  car- 
bon dioxide  are  simultaneously  eliminated  from  the  molecule, 
whereupon 

CH3.CO          CO.CH3 


2Cv 


/C 

O/ 


should  result.     The  tautomeride, 

HO  OH 
/    \ 

CH3-C  C-CHg 

II      II 

H-C       C-H 

Nc/ 

o 

however,  is  formed,  and  loses  one  molecule  of  water,  yielding  di- 
methylpyrone. 

Dimethylpyrone  is  characterized  by  its  ability  to  form  addition- 
products  with  acids,  which  must  be  looked  upon  as  salts.  These 
"salts"  are  formed  by  dissolving  dimethylpyrone  in  an  aqueous 
solution  of  hydrochloric  acid,  oxalic  acid,  etc.:  they  are  obtained 
in  a  crystalline  form  by  the  spontaneous  evaporation  of  the  solu- 
tions. By  dissolving  them  in  a  large  quantity  of  water,  they  are 
completely  hydrolyzed.  COLLIE  and  TICKLE,  the  discoverers 
of  these  compounds,  assume  the  quadrivalency  of  the  oxygen  atom 
closing  the  carbon  chain,  thus  attributing  to  dimethylpyrone 
hydrochloride  the  structure. 


C-OH      \O-C1. 
\  " 

\CH-C.  CH3 


314  ORGANIC  CHEMISTRY.      ,  [§239 

This  mode  of  expressing  the  constitution  of  dimethylpyrone  has 
been  adopted  instead  of  the  earlier  formula  COC4H2(CH3)2>  0  <^, 

VON  BAEYER  having  proved  the  addition-product  of  dimethylpyrone 
with  methyl  iodide  to  have  formula  I.,  and  not  formula  II.,  his  proof 
being  based  on  the  conversion  of  the  addition-product  by  the  action 
of  ammonia  into  methoxylutidine  (389),  formulated  in  III.: 


O-I  O  N 

CH3-C      C-CH3  CH3-C      OCH3  CH3-C      C-CH3 

II       I  II       II  II       I 

HC      CH  HC      CH  HC      CH 

\/  \/  \/ 

OOCH3  CO  C-OCH3 

I.  II.  III. 

These  compounds  have  been  named  oxonium  salts,  on  account 
of  their  analogy  to  the  ammonium  salts.  They  are  to  be  regarded 
as  true  salts  or  electrolytes,  because  they  possess  all  the  properties 
characteristic  of  the  salts  formed  by  weak  bases  with  strong 
acids:  thus,  their  aqueous  solutions  are  strongly  acidic  in  reaction 
in  consequence  of  extensive  hydrolytic  dissociation;  their  electric 
conductivities  in  solution  are  almost  equal  to  those  of  the  free 
acid;  and  so  on. 

The  power  of  forming  oxonium  salts  does  not  seem  to  be  limited 
to  dimethylpyrone  and  analogous  compounds.  VON  BAEYER  and 
VILLIGER  have  shown  that  oxygen-containing  compounds,  belong- 
ing to  various  classes  of  organic  bodies,  such  as  alcohols,  aldehydes, 
esters,  and  other  substances,  are  able  to  yield  crystalline  com- 
pounds with  complex  acids,  such  as  hydroferrocyanic  acid.  It  is 
possible,  though  not  fully  established,  that  these  are  oxonium  salts. 
They  also  attempted  to  obtain  trimethyloxonium  iodide,  (CH3)3O  •  I; 
analogous  to  the  tetra-alkylammonium  salts,  but  were  unsuccessful. 
They  are  of  opinion  that  GRIGNARD'S  compounds  of  alkyl  magne- 
sium iodides  and  ether  (75),  such  as  GHa-Mg-I-p-  ^Efe^O,  must 
be  regarded  as  oxonium  derivatives, 

C2H5>0<MgI_ 
" 


§239]  PYRONE  DERIVATIVES.  315 

The  power  of  forming  true  salts  by  the  addition  of  acids  is 
especially  developed  in  the  alkyl-compounds  of  the  elements  of  the 
nitrogen  group.  Examples  also  occur  among  the  sulphur  com- 
pounds (59).  Carbon  compounds  of  the  type  R3C-OH  also 
exhibit  basic  properties,  tertiary  aliphatic  alcohols  reacting 
readily  with  hydrogen  halides  to  form  tertiary  halogen  derivatives. 
The  replacement  of  the  hydroxyl-group  by  halogen  is  completely 
analogous  to  the  production  of  salts  by  the  interaction  of  bases 
and  acids. 


AMINO-ACIDS. 

240.  The  amino-acids  contain  one  or  more  ammo-groups  in 
direct  union  with  carbon.  They  are  of  physiological  import- 
ance, since  many  are  decomposition- products  of  proteins,  and 
some  are  natural  products.  They  are  synthesized  by  several 
methods. 

1.  By  the  action  of  the  halogen-substituted  fatty  acids  on 
ammonia,  a  method  analogous  to  the  formation  of  amines: 

H2N[H+CJlHaC.  CQQH  =  H2N.CH2-COOH+HC1. 

2.  By  reduction  of  oximes  with  sodium  amalgam: 
R.C(NOH).COOH+4H  =  R.CHNH2.COOH+H2O. 

This  is  a  method  of  converting  ketonic  acids  into  amino-acids. 

3.  a-Amino-acids  are  formed  by  the  action  of  ammonia  upon 
the  cyanohydrins  of  aldehydes  or  ketones,  and  subsequent  hydrol- 
ysis of  the  nitrile-group  (STRECKER)  : 


TT  .  TT 

CH3.C/    -*CH3.C^OH;     +NH3 
XO  \CN 

Acetaldehyde  Lactonitrile 

/H  /H 


v          -i^A-a.^  '    v-/jL_a.^  \  A  * 

\CN  \COOH 

Alanine  nitrile  Alanine 

The  amino-acids  possess  two  opposite  characters:  they  form 
salts  with  both  bases  and  acids,  and  are  therefore  both  basic  and 
acidic  simultaneously. 

Replacement  of  the  hydrogen  of  the  ammo-group  by  radicals 
yields  amino-acids  of  a  more  complicated  character.  Thus,  like 

316 


§  241]  AMINO-ACIDS.  317 

ammonia,  with  acid  chlorides  they  yield  an  acid  amide  with  one 
hydrogen  atom  of  the  amino-group  replaced : 

R.CO|C1+H|HN*CH2.COOH  =  R-CO-NH-CHa-COOH+HCl. 

Compounds  of  this  kind  are  therefore  both  amino-acids  and  acid 
amides. 

Amino-acids  with  the  hydrogen  of  the  amino-group  replaced 
by  alkyl-groups  are  also  known.  They  are  obtained  by  the  action 
of  amines,  instead  of  ammonia,  on  the  halogen-substituted  acids: 

(CH3)2N  [H+Cll  H2C  •  COOH  =  (CH3)2N.CH2.COOH+HC1. 

The  amino-acids  undergo  most  of  the  decompositions  charac- 
teristic of  amines;  thus,  with  nitrous  acid  they  yield  hydro  xy- 
acids,  just  as  the  amines  yield  alcohols. 

241.  Like  those  of  the  halogen-substituted  acids  and  hydroxy- 
acids  (176  and  180),  the  properties  of  the  amino-acids  depend  on 
the  position  of  their  characteristic  group — the  amino-group — 
relative  to  the  carboxyl-group.  The  a-amino-acids  readily 
yield  anhydrides  (acid  amides)  by  the  elimination  of  two  mole- 
cules of  water  from  two  molecules  of  acid : 


CH2  •  NH1H    HO  IOC  CH2NH  .  OC 

I     , I       =  2H20+|  |     . 

CO|OH  H|HNCH2  CO HNCH2 

The  /?-amino-acids  easily  lose  ammonia,  with  formation  of 
unsaturated  acids.  Thus,  /?-aminopropionic  acid,  obtained  from 
^-iodopropionic  acid,  is  converted  by  heat  into  acrylic  acid  and 
ammonia : 

iNHal-  CH2 •  CHjH]  -  COOH  =  NH3+CH2:CH.COOH. 

Like  the  f-hydroxy-acids,  the  ^--ammo-acids  yield  inner  anhy- 
drides. On  account  of  their  similarity  to  the  lactones,  these  sub- 
stances are  called  lactams: 

CH2  •  CH2  -  CH2  •  CO  CH2 .  CH2 .  CH2 .  CO 


L   =  H2o  + 

NH|H  OH  |  NH—  — J 

f-Aminobutyric  acid  Lactam  of  j--aminobutyric  acid 


318  ORGANIC    CHEMISTRY.  [§242 

EMIL  FISCHER  proved  that  the  esters  of  amino-acids  can  be 
obtained  by  the  ordinary  method,  dissolving  the  acids  in  absolute 
alcohol  and  treating  this  solution  with  hydrochloric-acid  gas  (91). 
Hydrochlorides  are  the  primary  products,  the  amino-group  in  these 
esters  retaining  its  basic  character:  an  example  is  the  ethyl  ester  of 
glycine  hydrochloride,  C2H5OOC  -  CH2  •  NH2  •  HC1.  The  esters  are 
prepared  by  treating  aqueous  solutions  of  the  hydrochlorides  with 
concentrated  potassium  hydroxide  at  a  low  temperature,  and  im- 
mediately extracting  with  ether.  EMIL  FISCHER  found  these  esters 
well  adapted  for  the  purification  and  separation  of  amino-acids. 
This  is  of  great  importance  in  the  chemistry  of  proteins,  which  are 
resolved  into  a  mixture  of  such  acids  by  the  action  of  acids  or  bases. 

Individual  Members. 

242.  Glycine  (glycocoll  or  aminoacetic  acid),  NH2-CH2'COOH, 
can  be  obtained  by  boiling  glue  with  dilute  sulphuric  acid  or  with 
barium  hydroxide:  it  owes  the  name  "glycocoll  "  to  this  method 
of  formation,  and  to  its  sweet  taste  (y\vKvs,  sweet;  Ko'XXa,  glue). 
It  is  also  prepared  from  hippuric  acid,  a  constituent  of.the  urine  of 
horses.  Hippuric  acid  is  glycine  with  one  hydrogen  atom  of  the 
amino-group  replaced  by  benzoyl,  C6H5CO;  and  it  therefore  has  the 
formula  C6H5.CO.NH.CH2.COOH.  Like  all  acid  amides,  it  is 
decomposed  by  boiling  with  dilute  acids,  with  addition  of  the  ele- 
ments of  water: 


C6H5CO. 
OH 


NH.CH2.COOH  =  C6H5.COOH+NH2.CH2.COOH. 


Benioic  acid  Glycine 

Hippuric  acid 

Glycine  can  be  synthetically  prepared  by  the  action  of  ammonia 
on  monochloroacetic  acid. 

Glycine  is  a  crystalline  solid,  and  melts  at  232°  with  decom- 
position: it  is  very  readily  soluble  in  water,  and  insoluble  in  abso- 
lute alcohol.  Like  many  amino-acids,  it  forms  a  well-crystallized, 
blue  copper  salt,  soluble  with  difficulty  in  water,  and  obtained  by 
boiling  copper  carbonate  with  a  solution  of  glycine.  This  derivative 
crystallizes  with  one  molecule  of  water  of  crystallization,  and  has 
the  formula  (NH2.CH2.COO)2Cu+H2O. 

Betame,  C5HnO2N,  is  a  derivative  of  trimethylglycine:  it  is 
found  in  the  juice  of  the  sugar-beet,  and  accumulates  in  the  molasses 
during  the  manufacture  of  sugar.  It  is  an  inner  ammon ium  salt, 


§242]  AMIXO-ACIDS.  319 

(CH3)3N.CH2.CO 


O[H       OH] 

since  it  is  synthetically  obtained  from  trimethylamine  by  the  action 
of  monochloroacetic  acid,  with  elimination  of  HC1: 

(CH3)3N   +  C1.CH2-COOH=(CH3)3N.CH2.CO 

I 6 

[ci~    "HI 


This  reaction  is  analogous  to  the  interaction  of  alkyl  halides  and 
tertiary  amines  to  form  the  salts  of  quaternary  ammonium  bases 

(63).  ' 

Betai'ne  yields  large  crystals  with  one  molecule  of  water,  which 
it  loses  at  100°,  or  when  allowed  to  stand  over  sulphuric  acid.  On 
heating  it  decomposes,  with  formation  of  trimethylamine. 

Many  tertiary  amines  can  be  converted  into  substances  with  a 
constitution  analogous  to  that  of  betai'ne;  that  is,  inner  salts  of 
ammonium  bases.  These  compounds  are  called  betames. 

Alanine,  or  a-aminopropionic  acid,  CH3'CH(NH2)*COOH,  is 
synthetically  prepared  by  the  action  of  ammonia  on  a-chloropropi- 
onic  acid. 

Leucine,  or  a-amino^sobutylacetic  acid, 

(CH3)2CH  •  CH2 .  CH  (NH2)  •  COOH, 

results  along  with  glycine  from  the  decomposition  of  proteins  by 
the  action  of  acids  or  alkalis,  or  by  putrefaction.  It  is  synthetic- 
ally obtained  from  isovaleraldehyde-ammonia  by  the  action  of 
hydrocyanic  acid,  and  hydrolysis  of  the  resulting  nitrile: 


(CH3)2CH  •  CH2  •  (%-  [OH  +  H  [CN  -» 
NH2 

zsoValeraldehyde-ammonia 

-»  (CH3)2CH.CH2.CH(NH2).CO2H. 

Leucine 

isoLeucine,  or  a-amino-/?-methyl valeric  acid, 
p^J  >CH.CH(NH2).COOH, 

^2xl5 

is  also  a  decomposition-product  of  proteins.     Its  constitution  is 


320  ORGANIC  CHEMISTRY.  [§243 

proved  by  synthesis.  The  aldehyde  formed  by  oxidation  of 
secondary  butylcarbinol  —  the  optically  active  amyl  alcohol  — 
yields  by  the  method  of  240,  3,  an  amino-acid  identical  with 
isoleucine. 

Fusel-oil  is  a  by-product  in  the  alcoholic  fermentation  (43). 
ERHLICH  has  proved  that  it  is  not  derived  from  the  sugars, 
but  from  leucine  and  isoleucine  formed  by  decomposition  of  the 
proteins  present  in  the  fermenting  liquid.  These  proteins  are  con- 
stituents of  the  grain,  potatoes,  and  other  material  employed  in 
the  manufacture  of  alcohol.  When  sugar  is  fermented  with  a  pure 
yeast-culture  in  presence  of  leucine,  tsobutylcarbinol  is  formed  as  a 
by-product:  with  tsoleucine  secondary  butylcarbinol  results. 
These  two  amyl  alcohols  are  the  principal  constituents  of  fusel-oil 
(47). 

The  mechanism  of  the  decomposition  of  amino-acids  by  yeast, 
or  their  alcoholic  fermentation,  is,  in  general,  expressed  by  the 
equation 

R-CH(NH2)-COOH+H2O  =  R-CH2OH+C02+NH3. 
The  leucine  obtained  from  proteins  is  optically  active:  its  for- 
mula contains  an  asymmetric  carbon  atom. 

243.  Asparagine  is  often  present  in  sprouting  seeds;  to  the  ex- 
tent of  20-30  per  cent,  in  dried  lupine-seeds.   It  is  aminosuccinamic 

PONTT 
acid,C2H3(NH2)  <2'  smce  on  nydrolys^s  ^  *s  converted  into 


aminosuccinic  acid  (aspartic  acid),  COOH.CH(NH2)-CH2.COOH, 
the  structure  of  which  is  inferred  from  its  conversion  into  malic 
acid  by  treatment  with  nitrous  acid.  Asparagine  prepared  from 
seeds  is  sometimes  dextro-rotatory,  but  generally  Isevo-rotatory. 
The  former  is  sweet,  the  latter  tasteless. 

Homologous  with  asparagine  is  glutamine,  a  constituent  of  the 
seeds  of  sprouting  plants.  It  is  the  amic  acid  (163)  of  ct-amino- 
glutaric  acid,  COOH.CH(NH2).CH2.CH2.COOH. 

In  addition  to  the  monoamino-acids,  diamino-acids  are  also 
obtained  by  decomposing  proteins  with  acids.  Some  of  them 
merit  description. 

Lysine,  C6Hi4O2N2,  is  decomposed  by  putrefaction-bacilli  with 
formation  of  pentamethylenediamine  (159):  it  has  the  formula 

NH2.CH2.(CH2)3-CH<£0(jH,  and  is  an  a£-aminocaproic  acid. 


f  244]  THE  WALDEN  INVERSION.  321 

EMIL  FISCHER  has  proved  this  formula  by  synthesis.  On  bring- 
ing etli3rl  monosodiomalonate  into  contact  with  7-chlorobutyro- 
nitrile,  ethyl  y-cyanopropylmalonate  is  formed : 

(COOC2H5)2CHNa  +C1  •  CH2  -  CH2  -  CH2  -  CN     -* 

Ethyl  monosodiomalonate  7-Chlorobutyronitrile 

->    (COOC2H5)2CH  •  (CH2)3  •  CN. 

Ethyl  v-cyanopropylmalonate 

Treatment  with  ethyl  nitrite  and  sodium  ethoxide  converts  this 
ester  by  elimination  of  a  carbethoxyl-group  into  the  sodium  salt  of 
.an  oxime: 


Oxime 

Reduction  of  this  oxime  with  sodium  and  alcohol  converts  the  NOH- 
group  into  NH2,  and  the  CN-group  into  CH2NH2,  with  formation  of 
inactive  lysine, 

CH2NH2.(CH2)3.CH<1VT 

Ornithine  is  the  next  lower  homologue  of  lysine,  and  has  the 
formula  C5H12O2N2  or  NH2.CH2.CH2.CH2.CH(NH2)  -COOH.  Bac- 
teria convert  it  into  putrescine  or  tetramethylenediamine  (159)- 
Its  structure  is  proved  by  EMIL  FISCHER'S  synthesis  (349). 

THE  WALDEN  INVERSION. 

244.  When  one  group  attached  to  an  asymmetric  carbon  atom 
is  replaced  by  another,  it  is  impossible  to  predict  the  sign  of  the 
rotation  of  the  new  compound:  sometimes  it  is  the  same  as  that 
of  the  original  substance,  and  sometimes  opposite  to  it.  By  a 
series  of  substitutions,  WALDEN  has  transformed  an  optically  active 
compound  into  its  optical  antipode.  On  treatment  with  moist 
silver  oxide,  Z-chlorosuccinic  acid  was  converted  into  Z-malic  acid, 
and  this  substance  was  transformed  by  means  of  phosphorus  penta- 
chloride  into  d-chlorosuccinnic  acid  On  the  other  hand,  starting 
from  d-chlorosuccinic  acid,  the  same  operation  yielded  /-chlorosuc- 
cinic  acid.  These  transformations  are  indicated  in  the  cyclic  scheme 

AgOH 
/-Chlorosuccinic  acid »/-Malic  acid- 


PC1'        AgOH  PC1< 

d-Malic  acid< -cZ-Chlorosuccinic  acid. 


ORGANIC  CHEMISTRY.  [§244 

Obviously,  a  transposition  of  the  groups  attached  to  the  asymmetric 
carbon  atom  is  induced  either  by  the  moist  silver  oxide  or  by  the 
phosphorus  pentachloride. 

The  following  is  another   reaction-cycle,  worked   out   by  EMIL 
FISCHER  : 

NOBrv 
d-Alanine —         — »Z-Bromopropionic  acid. 

JNH,  NOBr         JNH, 

d-Bromopropionic  acid<— — J-Alanine. 

Here  the  transposition  probably  took  place  during  the  replacement 
of  the  amino-group  by  bromine  under  the  influence  of  nitrosyl 
bromide,  and  not  by  the  action  of  ammonia,  since,  with  widely 
different  experimental  conditions,  the  same  product  with  a  similar 
sign  of  rotation  always  resulted  in  the  latter  operation.  Although 
d-alanine  reacted  with  nitrosyl  bromide  to  form  /-bromopropionic 
acid,  its  ester  under  identical  conditions  yielded  d-bromopro- 
pionic  acid. 

SENTER  has  discovered   many  other   examples  of  the  WALDEN 
inversion,  and  demonstrated  the  complex  nature  of  the  phenomenon. 


COOH 

AgOH 

I.  II.  1III.  IV. 

FIG.  70. — WERNER'S  THEORY  OF  THE  WALDEN  INVERSION. 

WERNER  has  put  forward  a  hypothesis  in  explanation  of  this 
inversion.  On  treatment  of  a-bromopropionic  acid  (I.)  with 
silver  hydroxide,  the  reaction  can  take  place  in  two  different  ways. 
One  of  them  involves  direct  action  on  the  bromine  atom,  and  its 
replacement  by  the  hydroxyl-group.  The  lactic  acid  thus  formed 
has  the  same  configuration  as  a-bromopropionic  acid,  and  the 
reaction  does  not  exemplify  the  WALDEN  inversion.  Replacement 
of  the  hydroxyl-group  by  bromine  by  means  of  phosphorus  penta- 
bromide,  or  otherwise,  regenerates  the  original  acid. 

In  the  other  type  of  reaction,  the  silver  hydroxide  attacks  the 
molecule  as  indicated  in  I.  On  elimination  of  silver  bromide,  the 
hydroxyl-group  does  not  replace  the  bromine  atom,  but  takes  up 
a  position  intermediate  between  the  other  groups,  causing  a  rear- 
rangement of  the  other  three  bonds,  as  indicated  in  II.  On 


§245]  ETHYL  DIAZO  ACETATE.  323 

replacing  the  hydroxyl-group  by  bromine  by  the  aid  of  phosphorus 
pentabromide  or  some  other  reagent,  a  substance  of  formula  III. 
is  obtained.  It  is  the  optical  antipode  of  I.,  as  is  proved  by 
rotating  III.  through  180°,  the  resulting  configuration  being  repre- 
sented by  IV.  In  this  instance,  a  WALDEN  inversion  has  taken  place. 

ETHYL  DIAZOACETATE. 

245.  CURTIUS  has  obtained  a  yellow  oil  of  characteristic  odour 
by  the  action  of  nitrous  acid  on  the  ethyl  ester  of  glycine:  this 
substance  has  the  formula  C4H602N2,  and  explodes  when  heated. 
TKe  method  of  its  formation  is  indicated  in  the  following  equation: 


+2H2O. 

Glycine  ethyl  ester  Nj 

It  is  ethyl  diazoacetate,  and  is  also  called  diazoacetic  ester. 

The  structural  formula  indicated  is  proved  by  numerous  trans- 
formations: they  can  be  classified  in  three  divisions. 

I.  The  first  group  includes  the  reactions  involving  the  elimina- 
tion of  the  diazo-nitrogen.  As  an  example  may  be  cited  the 
conversion  of  ethyl  diazoacetate  into  ethyl  glycollate  by  treat- 
ment with  dilute  acids: 


C2H5OOC.CH 


X 


N 


C2H5OOC.CH<f       +  N 
XOH 


BREDIG  discovered  that  this  reaction  is  greatly  accelerated  by 
the  catalytic  agency  of  hydrogen  ions,  and  on  this  observation  he 
has  based  one  of  the  best  methods  for  the  detection  and  quan- 
titative estimation  of  such  ions. 

Concentrated  hydrochloric  acid  yields  analogously  ethyl 
monochloroacetate,  and  iodine  ethyl  di-iodoacetate.  Organic  acids 
produce  acidylglycollic  acid  esters: 

H    N\ 
CH3-COO+||/CH.COOC2H5  =  CH  -COQ>CH-COOC2H5+N2. 


324  ORGANIC  CHEMISTRY.  [§245 

Near  its  boiling-point  ethyl  diazoacetate  loses  all  its  nitrogen, 
with  formation  of  ethyl  fumarate: 

CH.COOC2H5 
2N2CH  •  COOC2H5  =  2N2  +  1  ! 

CH.COOC2H5 

II.  In   the   second   group   of   reactions   the   nitrogen   is   not 
evolved  as  gas,  but  one  of  the  bonds  between  the  diazo-group  and 
carbon  is  severed,  with  formation  of  pyrazole-derivatives  (399)  . 

III.  The  third  group  comprises  addition-reactions  involving 
the  transformation  of  the  double  bond  between  the  nitrogen  atoms 
into  a  single  bond.     An  example  is  the  addition  of  hydrogen  to 
form  hydrazinoacetic  acid,  a  compound  decomposed  by  acids  at 
the  ordinary  temperature  into  glyoxylic  acid  and  a  hydrazine  salt: 


V 

>CH  .  COOH  +  H2SO4  +  H2O  =  N2  H4  -  H2SO4  +  CHO  .  COOH. 
NET 

Hydrazinoacetic  acid  Hydrazine  Glyoxylic  acid 

sulphate 

The  hydrogen  atom  of  the  CHN2-group  is  replaceable  by 
metals,  sodium  dissolving  in  ethyl  diazoacetate  with  evolution 
of  hydrogen. 


PROTEINS. 

246.  Proteins  are  compounds  of  great  importance  in  the 
animal  and  vegetable  kingdoms,  but  of  such  complex  structure 
that  their  chemical  investigation  is  a  matter  of  extreme  difficulty. 
Their  great  physiological  importance  is  made  apparent  by  the 
fact  that  the  dry  material  in  animal  bodies — apart  from  the 
mineral  constituents  and  fats — consists  almost  wholly  of  pro- 
teins, by  their  being  an  essential  constituent  of  each  living 
plant-cell,  and  by  their  forming  the  most  important  part  of 
human  and  animal  food.  An  animal  can  exist  without  fats 
and  carbohydrates  for  a  protracted  period,  but  its  death  is 
assured  by  the  withdrawal  of  proteins  from  its  nourishment. 

The  investigation  of  the  proteins  is  rendered  difficult  not  only 
by  their  complex  structure,  but  also  by  the  fact  that,  with  few 
exceptions,  they  do  not  crystallize,  and  cannot  be  distilled  without 
undergoing  decomposition,  so  that  advantage  cannot  be  taken  of 
these  valuable  aids  in  the  isolation  of  individual  substances. 
Moreover,  many  proteins  change  very  readily  into  other  sub- 
stances, and  the  distinctions  between  the  different  varieties  are 
sometimes  by  no  means  well  denned. 

A  number  of  groups  of  nitrogenous  compounds  are  classed  as 
proteins.  Since  they  sometimes  exhibit  great  differences  in 
physical  and  chemical  behaviour,  it  is  necessary  first  to  state  the 
general  properties  characteristic  of  them.  They  contain  only 
five  elements,  and  do  not  differ  much  from  one  another  in  com- 
position, as  the  table  indicates. 

Carbon 50-55     per  cent. 

Hydrogen 6  •  5-7  •  3 

Nitrogen 15-17-6       " 

Oxygen 19-24 

Sulphur 0-3-5 

Those  of  one  variety,  called  phospho-proteins,  also  contain  phos- 
phorus. 325 


326  ORGANIC  CHEMISTRY.  [§  247 

The  solutions  of  all  proteins  are  optically  active  and  Isevo- 
rotatory.  The  proteins  are  colloids  ("  Inorganic  Chemistry/'  196) ; 
they  are,  therefore,  unable  to  diffuse  through  parchment-paper. 
Advantage  is  often  taken  of  this  property  in  separating  them  from 
salts  and  other  crystalloids  (loc.  cit.).  Some  of  them  have  been 
obtained  crystalline,  among  them  serum-albumin:  most  of  them 
are  white,  amorphous  powders  without  definite  melting-points. 
On  heating,  they  carbonize,  with  evolution  of  gases. 

Many,  but  not  all  proteins  can  be  "  salted  out  "  from  solution. 
This  "  salting-out  "  is  an  important  aid  in  identifying  and  separat- 
ing the  different  varieties:  usually  common  salt  or  magnesium 
sulphate  is  employed.  It  is  remarkable  that  all  proteins  can  be 
completely  salted  out  from  their  solutions  in  both  neutral  and  acid 
liquids  by  saturation  with  ammonium  sulphate.  The  albumins 
can  be  fractionally  precipitated  from  aqueous  solutions  by  gradu- 
ally increasing  the  concentration  of  the  ammonium-sulphate  solu- 
tion. The  point  of  concentration  at  which  a  salt  begins  to  pre- 
cipitate a  protein  is  just  as  characteristic  for  the  latter  as,  for 
example,  the  solubility  is  for  a  crystalline  substance.  When  the 
salting-out  is  effected  at  ordinary  temperatures,  it  causes  no  change 
in  the  properties  of  the  proteins :  their  solubilities  after  the  opera- 
tion are  the  same  as  before  it. 

247.  Addition  of  alcohol  precipitates  proteins  unchanged  from 
aqueous  solution :  strong  alcohol  coagulates  them,  as  also  does  boil- 
ing with  water.  For  each  albumin  there  is  a  definite  coagulation- 
point:  in  other  words,  each  albumin  coagulates  at  a  definite 
temperature.  On  coagulation,  the  differences  in  solubility 
between  the  proteins  vanish:  all  are  rendered  insoluble  in  neutral 
solvents,  and  can  be  brought  into  solution  again  only  by  treatment 
with  dilute  caustic  alkalis  or  with  mineral  acids.  A  solution, 
which  behaves  exactly  like  the  solutions  thus  obtained,  can  be 
prepared  by  boiling  uncoagulated  albumins  with  a  large  excess  of 
acetic  acid  or  caustic  alkali. 

In  this  process  the  albumins  undergo  a  change  called  denatura- 
tion.  They  cease  to  be  coagulable  by  heat,  but  their  composition 
remains  unaltered.  The  products  are  called  meta-protems.  When 
the  hydrolysis  was  effected  with  alkali,  the  product  was  formerly 
termed  an  albuminate  or  alkali-albumin,  when  an  acid  was  em- 
ployed, a  syntonin  or  acid-albumin.  The  meta-proteins  are 


§  248]  PROTEINS.  327 

insoluble  in  water,  but  soluble  in  dilute  acids  and  alkalis.  They 
are  precipitated  by  neutralizing  their  solutions. 

The  proteins  are  precipitated  from  solution  by  various  sub- 
stances, either  by  coagulation  or  by  the  formation  of  compounds 
insoluble  in  water.  Coagulation  is  effected  by  the. addition  of 
mineral  acids,  preferably  nitric  acid. 

The  formation  of  compounds  insoluble  in  water  results  on 
addition  of  salts  of  most  of  the  heavy  metals,  especially  copper 
sulphate,  ferric  chloride,  and  an  acidified  solution  of  mercuric 
chloride.  The  proteins,  therefore,  behave  like  weak  acids,  which 
with  the  oxides  of  these  metals  yield  compounds  of  the  nature  of 
salts. 

Some  weak  acids  yield  insoluble  compounds  with  the  proteins, 
which,  therefore,  also  behave  as  bases:  in  this  respect  they  ex- 
hibit complete  analogy  to  their  main  decomposition-products,  the 
amino-acids.  Among  these  weak  acids  are  tanni&acid,  picric  acid, 
^phosphotungstic  acid,  and  others.  The  proteins  are  completely 
precipitated  from  solution  by  phosphotungstic  acid :  this  method, 
in  addition  to  coagulation  by  boiling,  and  precipitation  by  alcohol, 
is  employed  to  separate  dissolved  proteins  from  solution. 

Various  tests  for  proteins  are  known,  among  them  the  fol- 
lowing: • 

1.  Milton's  reagent,  a  solution  of  mercuric  nitrate  containing 
nitrous  acid,  yields  a  red,  coagulated  mass  on  boiling. 

2.  The  xanthoprotein-reaction  consists  in  the  formation  of  a 
yellow  coloration  on  treatment  with  warm  nitric  acid. 

3.  The  biuret-reaction  depends  upon  the  formation  of  a  fine 
red  to  violet  coloration  when  potassium  hydroxide  is  added  to  a 
protein,  and  then  a  two  per  cent,  solution  of  copper  sulphate  drop 
by  drop.     This   reaction   derives  its  name  from  the  fact  that 
biuret,  on  similar  treatment,  gives  the  same  coloration  (267). 

Nomenclature. 

248.  The  CHEMICAL  SOCIETY  OF  LONDON,  the  ENGLISH 
PHYSIOLOGICAL  SOCIETY,  the  AMERICAN  PHYSIOLOGICAL  SOCI- 
ETY, and  the  AMERICAN  SOCIETY  OF  BIOLOGICAL  CHEMISTS 
have  adopted  the  following  system  of  nomenclature  for  the 
proteins. 


328  ORGANIC  CHEMISTRY.  [§248 

1.  Protamines. — They   are   the    simplest    members    of    the 
group.    Examples   are  salmine  and   sturine,   isolated   from   fish- 
sperm. 

2.  Histones. — They  are  more  complex  than  the  protamines, 
but  probably  each  class  gradually  merges  into  the  other.     They 
are  exemplified  by  the  histories  separated  by  KOSSEL  from  blood- 
corpuscles.     Precipitability  by  ammonia  is  one  of  their  distin- 
guishing features. 

3.  Albumins. — Egg-albumin,  serum-albumin,  and  lad-albumin 
are  typical  examples. 

4.  Globulins. — They  differ  from  the   albumins  in  solubility. 
They  are  more  readily  salted  out  from  solution  than  the  albumins. 
Examples    are    serum-globulin,    fibrinogen,    and    such    globulin- 
derivatives  as  fibrin  and  myosin* 

5.  Glutelins. — Alkali-soluble    proteins    of    vegetable    origin. 
They  are  closely  related  to  the  globulins. 

6.  Gliadins. — Alcohol-soluble  proteins  found  in  the  vegetable 
kingdom.     The  principal  member  of  the  group  is  gliadin,   and 
ROSENHEIM  has  suggested  that  the   class  to  which  it  belongs 
should  be  designated  by  its  name. 

7.  Phospho-proteins. — Examples  are  vitellin,  casemogen  (the 
principal  protein  of  milk),  and  casein  (obtained  from  casei'nogen 
by  the  action  of  rennet).f 

8.  Sclero-proteins.t — This  class  includes  such  substances  as 
gelatin,  chondrin,  elastin,  and  keratin.     The  prefix  indicates  the 

*  The  carbohydrate-radical  separable  in  small  quantities  from  many  mem- 
bers of  Classes  3  and  4  is  probably  not  to  be  considered  as  a  "prosthetic 
group";  as  it  is  in  the  glucopro terns  (9,  c).  The  term  myosin  is  restricted 
to  the  final  product  formed  during  rigor  mortis.  VON  FURTH'S  "  soluble 
myogen-fibrin  "  should  be  called  soluble  myosin.  The  two  chief  proteins  of  the 
musc'e-plasma  are  termed  paramyosinogen  and  myosinogen. 

f  The  prefix  4<  nucleo-"  frequently  used  in  relation  to  this  class  is  incorrect 
and  misleading.  The  American  Societies  include  this  group  with  the  conju- 
gated proteins  (9).  Since  the  phosphorus-containing  radical  is  not  eliminated 
from  the  phospho-proteins  like  a  true  prosthetic  group,  and  their  cleavage- 
products  contain  phosphorus-,  the  English  Societies  prefer  the  arrangement 
indicated. 

J  This  term  replaces  the  word  "  albuminoid  "  in  the  limited  sense  in  which 
most  physiologists  have  employed  it,  but  the  American  Societies  retain  the 
old  name. 


§  248]  PROTEINS.  329 

skeletal  origin  of  its  members,  and  the  insolubility  of  many  of 
them. 

9.  Conjugated  Proteins.* — They  are  substances  in  which  the 
protein  molecule  is  united  to  a  prosthetic  group.     The  principal 
subdivisions  are 

a.  NUCLEO-PROTEINS. — An  example  is  guanylic  acid,  isolated 
from  the  pancreas,  liver,  spleen,  and  mammary  gland. 

b.  CHROMO-pROTEiNS.f — Hcemoglobin  is  a  type. 

c.  GLUCO-PROTEINS. — They  are  exemplified  by  the  mucins. 

10.  Protein-derivatives. % — They    comprise    the    products    of 
protein-hydrolysis,  and  are  classed  in  four  divisions. 

a.  META-PROTEINS. — This     group     includes     the     substances 
formerly  classed  as   "  albuminates  "   or  "  alkali-albumins/'   and 
"  syntonins  "  or  "  acid-albumins,"  obtained  by  the  action  of  an 
alkali  or  an  acid  respectively  on  albumins  and  globulins.     The 
name  meta-proteins  is  preferable  because   (1)   they  are  derived 
from  globulins  as  well  as  albumins,  and  (2)  the  termination  ate 
implies  a  salt. 

b.  PROTEOSES. — They  include   such  substances   as  albumose, 
globulose,  and  gelatose. 

c.  PEPTONES. — Further  products  of  hydrolysis  which  resemble 
the   proteins   in   answering   the   biuret-test,    but,    unlike   them, 
cannot  be  salted  out  from  solution. 

d.  POLYPEPTIDES. — Products  of  cleavage  beyond  the  peptone 
stage  containing  two  or  more  amino-acid-residues.     Most  of  them 
are  synthetical  substances,  but  some  of  them  have  been  separated 

*  The  American  Societies  add  "  lecitho-protems"  to  this  class,  but  their 
English  confreres  object  on  account  of  the  uncertainty  as  to  whether  these 
substances  are  mechanical  mixtures,  adsorption-compounds,  or  true  chemical 
combinations. 

t  The  American  Societies  employ  the  term  "Haemoglobins"  for  chromo- 
prote'ins. 

t  The  American  Societies  include  two  additional  classes  in  this  group: 
"proteans,"  insoluble  products  apparently  resulting  from  the  incipient 
action  of  water,  very  dilute  acids,  or  enzymes;  and  "coagulated  proteins," 
formed  by  the  action  of  heat  or  of  alcohol.  They  are  of  an  ill-defined  nature, 
and  the  English  Societies  consider  that  it  is  better  not  to  single  out  for  special 
mention  a  few  of  the  infinite  varieties  of  insoluble  modifications  exhibited  by 
proteins. 


330  ORGANIC   CHEMISTRY.  [§  249 

from  the  products  of  protein-hydrolysis.  Most  of  those  hitherto 
prepared  do  not  answer  the  biuret-test. 

249.   Particulars  of  some  of  the  classes  named  are  appended. 

The  albumins  are  the  best  known  and  most  readily  obtained 
of  the  proteins:  all  form  well-defined  crystals,  and  they  are 
therefore  probably  among  the  few  proteins  known  to  be  individual 
chemical  compounds;  although  it  has  not  been  proved  that  these 
crystals  are  not  mixed  crystals  containing  two  or  more  analogous 
individuals.  They  dissolve  in  water. 

Their  neutral  solutions  cannot  be  salted  out  with  sodium 
chloride,  magnesium  sulphate,  or  a  semi-saturated  solution  of 
ammonium  sulphate — a  method  of  separating  them  from  the 
globulins,  which  always  occur  along  with  them. 

The  globulins  are  further  distinguished  from  the  albumins  by 
being  insoluble  in  water,  although  they  dissolve  in  dilute,  neutral 
salt  solutions,  and  in  solutions  of  alkali-metal  carbonates.  At  30° 
they  can  be  completely  salted  out  by  magnesium  sulphate,  and 
partly  by  sodium  chloride.  They  have  not  been  obtained  crystal- 
line. 

The  phospho-protems  contain  phosphorus,  and  have  a  distinctly 
acidic  character.  All  of  them  turn  blue  litmus  red,  and  in  the 
free  state  they  are  only  slightly  soluble  in  water,  though  their 
alkali-metal  salts  and  ammonium  salts  are  freely  soluble.  The 
solutions  of  their  salts  do  not  coagulate,  and  can  be  boiled  without 
undergoing  any  change. 

The  sclero-protelns  differ  somewhat  in  character  from  the 
albumins.  They  occur  in  tho  animal  economy  only  in  the  undis- 
solved  state,  being  the  organic  constituents  of  the  skeleton  and 
the  epidermis.  They  include  various  substances,  such  as  keratin, 
elastin,  gelatin,  collagen,  and  chondrin. 

Keratin  is  the  principal  constituent  of  the  epidermis,  hair,  nails, 
hoofs,  and  feathers.  It  is  particularly  rich  in  sulphur,  of  which 
it  contains  between  four  and  five  per  cent.  Its  decomposition- 
products  resemble  those  of  the  albumins.  With  nitric  acid  it 
gives  the  xanthoprotei'n-reaction,  the  origin  of  the  yellow 
colour  developed  when  nitric  acid  comes  into  contact  with  the 
skin. 

Elastin  is  the  substance  constituting  the  fibres  of  connective 
tissue.  Its  decomposition-products  have  the  same  qualitative 


§250]  PROTEINS.  331 

composition  as  those  obtained  from  the  albumins.  It  is  insol- 
uble in  dilute  acids  and  caustic  alkalis. 

The  collagens  are  the  principal  sclero-protei'ns  of  the  animal 
body,  and  the  main  constituent  of  connective  tissue,  such  as  bone 
and  white  fibrous  tissue.  In  several  respects  they  differ  from 
the  albumins:  they  contain  17-9  per  cent,  of  nitrogen;  they 
have  not  an  aromatic  nucleus;  on  hydrolysis,  they  do  not  yield 
tyrosine  (352),  their  chief  decomposition-product  being  glycine, 
which  is  accompanied  by  leucine,  aspartic  acid,  and  glutamic 
acid. 

When  boiled  with  water,  the  collagens  are  transformed  into 
gelatin.  This  substance  is  not  precipitated  from  solution  by 
nitric  acid  or  other  mineral  acids,  but  it  is  precipitated  by 
mercuric  chloride  in  presence  of  hydrochloric  acid '  and  by  tan- 
nic  acid. 

Chondrin  is  obtained  by  extracting  cartilage  with  boiling  water, 
the  solution  gelatinating  as  it  cools.  Acetic  acid  precipitates 
chondrin  from  solution.  When  boiled  with  dilute  acids,  chondrin 
yields  a  decomposition-product,  chondrosin,  which  reduces  FEH- 
LING'S  solution.  Chondrin  is  a  derivative  of  gelatin  and  chon- 
droitinsulphuric  acid. 

In  the  inferior  ordcn  of  animal  life  a  series  of  substances 
has  been  discovered  approximating  more  or  less  closely  in  chemical 
properties  to  the  collagens  and  to  elastin.  Among  them  is  spongin, 
the  principal  constituent  of  sponges,  which  is  much  more  stable 
towards  caustic  soda  and  baryta-water  than  collagen.  When 
completely  hydrolyzed  by  boiling  with  dilute  sulphuric  acid,  it 
yields  leucine  and  glycine,  but  no  tyrosine,  proving  it  to  be  a 
collagen. 

On  prolonged  boiling  with  water,  silk  is  converted  into  fibroin, 
which  is  not  decomposed  by  water  even  at  200°,  and  sericin,  or 
silk-gum. 

Cornem  is  the  organic  constituent  of  coral.  On  hydrolysis, 
it  yields  leucine  and  an  aromatic  substance  of  unknown  com- 
position. 

250.  Nearly  related  to  the  albumins  are  the  conjugated  proteins, 
compounds  of  proteins  with  other  substances,  usually  of  a  very 
complex  nature.  Like  the  albumins,  they  are  insoluble  in  alcohol, 
by  which  most  of  them  are  coagulated. 


332  ORGANIC  CHEMISTRY.  [§  250 

Nudeo-protelns  derive  their  name  from  the  fact  that  they  are 
the  principal  constituents  of  the  cell-nuclei.  They  are  com- 
binations of  proteins  with  phosphoric  acid  or  nucleic  acids 
(Nucleus,  important  part  of  the  cells  of  animals  or  plants).  A 
nucleic  acid  is  phosphoric  acid  which  is  partially  saturated  by 
union  with  basic  substances,  such  as  hypoxanthine,  guanine, 
xanthine,  etc.  The  composition  of  the  nucleo-prote'ins  differs 
considerably  from  that  of  the  albumins:  they  contain  about 
41  per  cent,  of  carbon,  31  per  cent,  of  oxygen,  and  5-7  per  cent. 
of  phosphorus. 

The  nucleo-protems  have  a  markedly  acidic  character:  they 
are  soluble  in  water  and  very  soluble  in  caustic  alkalis.  They 
answer  to  the  protein  colour-tests. 

Chromo-proteins  are  compounds  of  proteins  with  substances 
containing  iron,  haemoglobin  being  the  dye  of  red  blood-corpuscles. 
It  decomposes  into  globin  and  hcematin.  In  the  lungs  it  unites 
readily  with  the  oxygen  of  respired  air,  yielding  oxyhcemoglobin. 
This  substance  readily  gives  up  its  oxygen,  and  thus  the  oxidation- 
processes  which  maintain  the  heat  of  the  animal  body  are  carried 
on.  It  unites  with  carbon  monoxide  to  form  carbonyl-hcemoglobin, 
which -is  unable  to  combine  with  oxygen:  on  this  reaction  depends 
the  poisonous  nature  of  carbon  monoxide. 

On  treatment  with  acetic  acid  and  sodium  chloride,  oxyhsemo- 
globin  yields  the  hydrochloride  of  haematin,  called  hcemin,  which 
crystallizes  in  characteristic,  microscopic  plates  of  a  brown-red 
colour.  The  reaction  furnishes  a  delicate  test  for  blood. 

Gluco-proteins  are  compounds  of  proteins  and  carbohydrates. 
They  include  the  mucins,  which,  like  the  nucleo-proteins,  are 
acidic  in  character.  They  are  insoluble  in  water,  but  soluble  in  a 
small  quantity  of  lime-water  or  alkali  solution.  The  liquid  thus 
obtained  is  neutral,  has  a  glutinous  appearance,  and  is  not  coagu- 
lated by  boiling.  Unlike  the  solutions  of  the  albumins,  these 
solutions  are  not  precipitated  by  nitric  acid.  When  boiled  with 
acids  or  caustic  alkalis,  they  yield  either  syntonins  or  peptones, 
together  with  carbohydrates.  The  presence  of  the  nitrogen-free 
carbohydrates  makes  the  percentage-amount  of  nitrogen  in  the 
mucins  considerably  less  than  in  the  albumins:  its  value  lies 
between  11  •  7  and  12-3  per  cent. 

Meta-proteins  are  mentioned  in  247. 


§251]  PROTEINS.  333 

Proteoses  and  peptones  can  be  obtained  from  all  proteins  by 
suitable  hydrolysis.  They  have  the  protein-character,  being 
insoluble  in  alcohol,  and  answering  the  xanthoproteiin-test  and 
biuret-test  (247,  2  and  3).  They  are  produced  during  digestion 
by  the  action  of  gastric  juice  on  proteins,  and  are  to  be  regarded 
as  intermediate  products  in  the  hydrolysis  of  proteins,  the  pro- 
teoses  being  nearer  the  proteins,  and  the  peptones  nearer  the 
amino-acids. 

The  Structure  of  the  Protein  Molecule. 

251.  During  last  century  experimental  evidence  of  the  complex 
structure  of  the  protein  molecule  was  accumulated,  an  important 
point  being  the  great  number  of  substances  formed  by  the  decom- 
position of  albumin.  On  dry  distillation  it  yields  a  black  oil 
containing  many  nitrogen  bases;  hydrocyanic  acid,  sulphuretted 
hydrogen,  carbon  dioxide,  water,  benzene,  and  its  homologues, 
and  numerous  other  bodies  being  also  formed.  Both  putrefaction 
and  fusion  with  potassium  hydroxide  yield  ammonia,  sulphuretted 
hydrogen,  volatile  fatty  acids  such  as  butyric  acid  and  valeric 
acid,  amino-acids  like  leucine  and  tyrosine,  scatole,  ptomaines, 
p-cresol,  and  other  products.  By  oxidation  with  various  agents 
it  has  been  possible  to  isolate  hydrocyanic  acid,  nitriles,  benzoic 
acid,  numerous  volatile  fatty  acids,  and  other  substances. 

New  products  have  resulted  from  each  fresh  mode  of  attack, 
but  the  analytical  methods  employed  have  not  shed  any  light  on 
the  structure  of  the  protein  molecule,  since  they  yield  chiefly 
amorphous  and  ill-defined  substances.  The  first  important  step 
towards  the  solution  of  the  problem  was  made  by  SCHUTZEX- 
BERGER  when  he  obtained  only  crystalline  derivatives  by  heating 
proteins  with  bartya-water  in  an  autoclave  at  200°  for  several 
hours.  After  removal  of  the  barium,  the  weight  of  the  decom- 
position-products formed  exceeded  that  of  the  initial  proteins, 
proving  that  the  baryta-water  had  effected  addition  of  the 
elements  of  water,  thus  hydrolyzing  the  proteins  to  crystalline 
derivatives. 

It  was  impossible  to  effect  complete  separation  of  the  very 
complex  mixture  thus  obtained,  but  some  of  the  less  soluble  con- 
stituents, such  as  leucine  and  tyrosine,  were  isolated.  The. 


334  ORGANIC  CHEMISTRY.  [§  252 

presence  in  the  reaction-product  of  a  number  of  amino-acids  was 
proved  by  its  properties  and  the  results  of  analysis.  SCHUTZEN- 
BERGER'S  brilliant  research  was  rendered  more  difficult  by  the 
necessity  of  making  several  hundred  analyses.  The  most  import- 
ant conclusion  to  be  drawn  from  it  is,  that  the  amino-acids  con- 
stitute the  foundation-stones  of  the  proteini,  just  as  the  monoses 
are  the  basis  of  the  polyoses  (225) .  The  fission-products  obtained 
by  earlier  experimenters  were  formed  by  decomposition  of  the 
amino-acids. 

252.  SCHUTZENBERGER  did  not  succeed  in  separating  the 
various  amino-acids  from  the  mixture  obtained  by  his  method  of 
fractional  crystallization,  but  the  identification  of  the  various 
amino-acids  derivable  from  the  individual  proteins  would  be 
insufficient  for  a  complete  comprehension  of  the  structure  of  the 
protein  molecule:  the  proportion  of  each  acid  must  also  be  deter- 
mined by  separation  of  the  complex  mixture  into  its  individual 
constituents.  By  esterification  of  the  amino-acids  (241)  and 
fractional  distillation  in  vacuo  of  the  mixture  of  esters,  EMIL 
FISCHER  succeeded  not  only  in  isolating  the  principal  constituents, 
but  also  in  attaining  an  approximate  insight  into  their  relative 
proportions  in  the  different  proteins.  His  classical  researches 
have  enabled  the  products  of  protein-hydrolysis  to  be  classified 
in  six  divisions. 

1.  Monobasic  monoamino-acids. — Glycine,   alanine,  a-amino- 
valeric  acid,  leucine  (242),  and  phenylalanine, 

C6H5.CH2.CHNH2.COOH. 

2.  Dibasic    monoamino-acids. — Aspartic  acid   and    glutamic 
acid  or  aminoglutaric  acid. 

3.  Diamino-acids. — Ornithine  and  lysine  (243).     In  the  same 
category  may  be  included  arginine,  obtained  by  addition  of  cyan- 
amide  to  ornithine  (270). 

4.  Hydroxyamino-acids. — Tyrosine  (352)  has  been  known  for  a 
long  time.     Of  more  recent  date  is  serine,  CH2OH  •  CHNH2  •  COOH, 
which  is  synthesized  from  glycollaldehyde : 

CH2OH  •  C^  +  HCN  ->  CH2OH  -  CH^  ; 
+  NH3^CH2OH.CHNH2.COOH  (240,  3). 

This  synthesis  indicates  the  constitution  of  serine,  and  further 
confirmation  is  afforded  by  its  reduction  to  a-alanine. 


§  252]  PROTEINS.  335 

To  this  class  also  belongs  the  complicated  diaminotrihydroxy- 
dodecanic  acid,  C^H^eC^^  a  docomposition-product  of  casein. 

5.  Compounds  with  a  closed  chain  containing  nitrogen. — a- 
Tetrahydropyrrolecarboxylic*    acid   or   proline,    and    hydroxytetra- 
hydropyrrolecarboxylic   acid   or   hydroxyprolin?,    are   examples    of 
such   derivatives.     Tryptophan    (403),    CnHi2O2N2,    contains    a 
similar  chain:  probably  scatole  (403)  which  causes  the  character- 
istic odour  of  human  faeces,  is  derived  from  this  fission-product 
of  proteins.     Tryptophan  is  characterized  by  the  formation  of  a 
violet   coloration   or  precipitate   on   addition   of   bromine-water. 

NH5CEL 
Histidine,   I  >C-CH2*CH(NH2)-COOH,  in  its  laevo-modifi- 

CH=X  / 

cation  is  a  degradation-product  of  almost  all  albumins.     Its  racemic 
form  has  been  synthesized,  and  resolved  into  its  optical  isomerides. 

6.  Compounds  containing  sulphur. — The  only  representative 
of  this  class  is  cystine,  C6Hi2O4N2S2,  which  as  early  as  the  begin- 
ning of  last  century  was  identified  by  WOLLASTON  as  the  principal 
constituent  of  certain  gall-stones.     It  has  the  formula 

COOH  •  CHNH2  •  CH2S— SCH2 .  CHNH2  •  COOH. 

On  reduction  it  is  converted  into  cysteme,  COOH.  CHNH2»  CH2SH; 
from  which  atmospheric  oxidation  regenerates  cystine. 

The  constitution  of  cystine  is  proved  by  its  formation  from  the 
benzoyl  ester  of  serine  (in  which  the  benzoyl-group  is  attached  to 
nitrogen) :  fusion  with  phosphorus  pentasulphide  converts  the 
CH2OH-group  in  this  ester  into  a  CH2SH-group.  On  elimination 
of  benzoyl,  cystei'ne  is  obtained. 

EMIL  FISCHER  has  found  that  the  hydrolysis  of  proteins  can 
be  more  readily  effected  by  boiling  with  concentrated  hydro- 
chloric acid,  or  sulphuric  acid  of  25  per  cent,  strength,  than  by 
SCHUTZENBERGER'S  baryta-water  method. 

EMIL  FISCHER'S  ester-method  has  rendered  possible  the 
approximate  quantitative  estimation  of  the  products  of  protein- 
hydrolysis.  In  the  following  brief  summary  of  the  results  ob- 
tained it  should  be  noted  that  usually  not  more,  and  often  less, 
than  70  per  cent,  of  the  protein  is  recovered  in  the  form  of 
definite  compounds,  there  being  a  considerable  residue  which 
cannot  be  identified  on  account  of  experimental  difficulties. 
*  Cf.  foot-note,  395. 


336 


ORGANIC  CHEMISTRY. 


[§253 


On  decomposition,  some  proteins  yield  almost  exclusively  a 
single  amino-acid.  Examples  of  such  relatively  simple  proteins 
are  salmine  and  clupelne,  isolated  by  KOSSEL  from  the  testicles 
of  the  salmon  and  herring  respectively.  On  hydrolysis  the  first 
yields  84-3  per  cent,  of  arginine,  and  the  second  82*2  per  cent. 

Usually,  however,  the  proteins  yield  a  series  of  ammo-acids, 
the  proportions  of  the  individual  constituents  varying  between 
wide  limits.  In  most  proteins  leucine  (242)  is  the  principal  con- 
stituent, as  in  haemoglobin  (250),  keratin,  and  elastin  (249).  It 
is  only  in  fibroin  and  in  gelatin  (249)  that  glycine  predomi- 
nates. Of  the  dibasic  amino-acids,  aspartic  acid  (243)  is  generally 
present  in  small  proportion.  Casein  (248,  7)  contains  a  relatively 
large  amount  of  glutamic  acid.  Tyrosine  is  the  principal  decom- 
position-product of  fibroin:  alanine  and  glycine  are  formed  in 
smaller  proportions.  Cystine  is  an  important  constituent  of 
keratin:  from  cow-hair  as  much  as  8  per  cent,  of  it  has  been 
obtained,  and,  on  hydrolysis,  human  hair  also  yields  a  large 
proportion. 

The  table  summarizes  the  percentage-composition  of  a  few 
proteins  with  respect  to  certain  constituents. 


Haemo- 
globin. 

Casein. 

Gelatin. 

Keratin 
(from  hair) 

Fibroin 

GlycinB                   ... 

o 

o 

16*5 

4-7 

1  1  Jilll 

Ala,nine                  .... 

4 

0-9 

0-8 

21 

27-8 

10-5 

2-1 

7-1 

1-5 

Aspartic  acid 

4-3 

1*2 

0-6 

1-7 

10-7 

0-9 

3-7 

Anrinine                  .... 

5-2 

4-8 

7-6 

1 

Histidin6           

10-5 

2-6 

0-4 

Tyrosine  

1-3 

4-5 

3-2 

10 

Proline     .       

2-3 

3»2 

5-2 

3-4 

Cystine            

0-3 

0-1 

8 

253.  Having  elucidated  the  basis  of  the  protein  molecule, 
EMIL  FISCHER  applied  himself  to  the  solution  of  the  greatest 
problem  of  organic  chemistry — the  synthesis  of  the  proteins.  It 
has  long  been  thought  that  the  amino-acids  of  the  protein  molecule 
are  linked  by  their  amino-groups,  as  in  glycylglycine, 


NH2  •  CH2  •  CO— NH  •  CH2 .  COOH, 


§253]  PROTEINS.  337 

in  which  the  amino-group  of  one  molecule  of  glycine  has  become 
united  with  the  carboxyl-group  of  another  molecule,  as  in  the 
formation  of  acid  amides.  This  hypothesis  was  confirmed  by 
the  researches  of  EMIL  FISCHER.  He  succeeded,  by  employing  a 
number  of  synthetic  methods,  in  uniting  various  amino-acid- 
residues,  and  named  the  resulting  compounds  polypeptides. 
They  display  great  analogy  to  the  natural  peptones  (248,  10,  c). 
Their  synthesis  proves  that  they  have  the  structure  indicated. 

It  is  not  possible  to  give  here  a  detailed  description  of  these 
synthetic  methods,  but  a  brief  review  will  not  be  out  of  place.  On 
heating,  the  esters  of  ami  no-acids  are  converted  into  anhydrides, 
with  elimination  of  two  molecules  of  alcohol,  the  reaction  some- 
times taking  place  even  at  ordinary  temperatures  : 


2NH2.CH2.COOC2H5  =  2C2H5OH  +  NH  <"7>  NH. 

Glycine  ethyl  ester  Diketopiperazine 

(Glycine  anhydride) 

Under  the  influence  of   dilute  caustic  potash,  this  anhydride  takes 
up  one  molecule  of  water,  yielding  a  dipeptide,  glycylglycine  : 


=  NH2.CH2.CO—  NH.CH2.COOH. 
x2  — 

Glycylglycine 

When  a  dipeptide  is  treated  with  phosphorus  pentachloride  in 
acetyl.  chloride  solution,  the  carboxyl-group  is  changed  to  COC1, 
and  the  residue  of  this  acid  chloride  can  be  introduced  into  other 
amino-acids  : 

NH2  .  CH2  .  CO—  NH  .  CH2  .  COC1  +  H2N  •  CH2  .  COOC2H5  = 
=  NH2  •  CH2  •  CO—  NH  •  CH2  .  CO—  NH  .  CH2  .  COOC2H5  +  HC1. 

Saponification  of  this  substance  yields  a  tripeptide,  and  so  on. 

The  polypetides,  especially  from  the  tetrapeptides  to  the 
octapeptides,  are  very  like  the  natural  peptones,  as  a  short  sum- 
mary of  the  characteristics  of  both  classes  will  indicate.  Most 
of  them  are  soluble  in  water,  and  insoluble  in  alcohol:  those 
less  soluble  are,  however,  readily  dissolved  by  acids  and  bases. 
They  usually  melt  above  200°  with  decomposition,  and  have  a 


338  ORGANIC  CHEMISTRY.  [§  254 

bitter  and  insipid  taste,  and  are  precipitated  by  phosphotungstic 
acid.  They  answer  the  biuret-test  (247,  3) :  for  the  poly- 
peptides  the  sensitiveness  of  the  reaction  augments  with 
increase  in  the  length  of  the  chain.  Boiling  with  concentrated 
hydrochloric  acid  for  about  five  hours  effects  complete  hydrolysis. 
At  ordinary  temperatures  they  are  stable  towards  alkalis.  They 
are  hydrolyzed  by  the  action  of  pancreatic  juice. 

The  highest  polypeptide  prepared  by  EMIL  FISCHER  is  an 
octadecapeptide  containing  eighteen  amino-acid-residues,  fifteen  of 
them  being  glycine-residues  and  three  being  leucine-residues.  It 
has  all  the  characteristics  just  enumerated,  and  had  it  been  first 
discovered  in  nature,  it  would  certainly  have  been  classed  as  a 
protein. 

This  octadecapeptide  has  the  molecular  weight  1213:  that  of 
most  of  the  fats  is  much  smaller,  the  figure  for  tristearin  being 
891.  It  is  the  most  complex  substance  of  known  structure 
hitherto  obtained  by  synthesis.  The  natural  proteins  are  prob- 
ably mixtures  of  various  polypeptides  for  which  no  mode  of 
separation  has  been  discovered. 

The  step-by-step  decomposition  of  fibroin  (249)  also  indicates 
that  the  amino-acids  in  the  proteins  have  an  amino-linking.  When 
it  is  treated  with  concentrated  hydrochloric  acid,  sericoin  results, 
and  is  converted  by  further  boiling  with  the  same  acid  into  a  peptone. 
Pancreatic  juice  converts  this  substance  into  tyrosine  (352),  and 
another  peptone,  which  answers  the  biuret-test.  On  warming 
this  second  peptone  with  baryta-water,  however,  it  no  longer  answers 
this  test,  and  a  dipeptide,  glycylalanine,  can  be  isolated  from  the 
products  of  decomposition. 

254.  Nothirg  is  known  about  the  molecular  weight  of  the 
proteins,  except  that  it  must  be  very  great.  Attempts  to  deter- 
mine it  by  the  cryoscopic  method  have  yielded  very  small 
depressions  of  the  freezing-point.  It  is  uncertain  whether  the 
observed  depressions  may  have  been  due  to  the  presence  of 
traces  of  mineral  salts  in  the  albumin  employed,  since  their  com- 
plete removal  is  a  difficult  operation.  The  negative  character 
of  the  results  might  also  be  due  to  the  presence  of  the  albumin  in 
the  colloidal  state,  since  colloids  produce  only  a  very  small  molec- 
ular depression  ("  Inorganic  Chemistry,"  196). 


§254]  PROTEINS.  339 

The  proportion  of  sulphur  in  the  proteins  supports  the  hypoth- 
esis of  a  high  molecular  weight.  In  some  varieties  it  is  about 
1  per  cent.  Since  there  cannot  be  less  than  1  atom,  or  32  parts 
by  weight,  of  sulphur  in  the  protein  molecule,  this  percentage 
points  to  a  molecular  weight  of  3200,  assuming  the  presence  of 
only  one  atom  of  sulphur  in  the  molecule.  The  percentage  of  iron 
in  haemoglobin  indicates  for  this  protein  a  molecular  weight  of 
about  12,500.  Other  data  give  10,000  as  the  approximate 
molecular  weight  of  many  proteins.  But  there  is  no  gainsaying 
the  fact  that  these  conclusions  rest  on  a  very  uncertain  basis:  the 
close  analogy  between  the  higher  polypeptides  and  the  natural 
proteins  makes  it  probable  that  the  chains  of  the  protein  molecule 
do  not  contain  more  than  about  20  amino-acid-residues. 

Even  if  the  difference  in  the  nature  and  in  the  number  of  the 
amino-acids  in  the  protein  molecule  is  alone  considered,  it  is 
evident  that  an  almost  infinite  variety  of  proteins  is  theoretically 
possible.  Assuming  that  the  protein  molecule  contains  20  different 
amino-acid-residues,  it  can  be  represented  by  the  scheme 


A  being  an  amino-acid-residue.  Each  fresh  grouping  of  these 
residues  produces  a  new  isomeride.  According  to  the  theory  of 
permutations,  there  are  possible  20Xl9Xl8X...X2xl  or 
approximately  2«3X1018  =  2«3  trillion  groupings,  and  hence  a 
like  number  of  isomerides.  For  other  reasons  this  number  must 
be  greatly  increased,  the  first  of  them  being  based  on  stereo- 
chemical  considerations.  Some  amino-acids  contain  asymmetric 
carbon  atoms:  if  the  protein  molecule  contains  n  of  them,  the 
number  of  stereoisomerides  possible  is  2n.  Assuming  that  the 
value  of  n  in  the  foregoing  example  is  10,  each  of  the  2-3  trillion 
substances  could  exist  in  210=1024  optically  isomeric  forms. 
The  second  reason  is  that  the  group  —  CO«XH  —  can  also  exist 
in  the  tautomeric  form  (235)  —  C(OH):N  —  .  It  is  evident  that 
the  number  of  possible  isomerides  is  almost  unlimited.  It  is  so 
great  as  to  make  it  possible  that  each  of  the  different  kinds  of 
living  material  has  its  own  individual  protein;  and  that  the 
infinite  variety  of  forms  found  in  organic  nature  is  partly  the 
result  of  isomerism  in  the  protein  molecule. 


CYANOGEN  DERIVATIVES. 


Cyanogen,  C2N2. 

255.  When  mercuric  cyanide,  Hg(CN)2,  is  heated,  it  decom- 
poses into  mercury,  and  a  gas,  cyanogen.  A  brown,  amorphous 
polymeride,  paracyanogen,  (CN)X,  is  simultaneously  formed:  on 
heating  to  a  high  temperature,  it  is  converted  into  cyanogen.  A 
better  method  for  the  preparation  of  cyanogen  is  the  interaction 
of  solutions  of  potassium  cyanide  and  copper  sulphate;  cupric 
cyanide  is  formed,  and  at  once  decomposes  into  cuprous  cyanide 
and  cyanogen: 

4KCN+2CuS04  =  2K2SO4+Cu2(CN)2  +  (CN)2. 

The  reaction  is  analogous  to  that  between  potassium  iodide  and 
a  solution  of  copper  sulphate,  from  which  cuprous  iodide  and  free 
iodine  result. 

Cyanogen  is  closely  related  to  oxalic  acid.  Thus,  when  ammo- 
nium oxalate  is  heated  with  a  dehydrating  agent,  such  as  phos- 
phoric oxide,  cyanogen  is  produced:  inversely,  when  cyanogen  is 
dissolved  in  hydrochloric  acid,  it  takes  up  four  molecules  of  water, 
with  formation  of  ammonium  oxalate.  These  reactions  prove 
cyanogen  to  be  the  nitrile  of  oxalic  acid,  so  that  its  constitutional 
formula  is  N=C— C=N. 

Cyanogen  is  also  somewhat  analogous  to  the  halogens,  as  its 
preparation  from  potassium  cyanide  and  copper  sulphate  indi- 
cates. Moreover,  potassium  burns  in  cyanogen  as  in  chlorine, 
with  formation  of  potassium  cyanide,  KCN;  and  when  cyanogen 
is  passed  into  caustic  potash,  potassium  cyanide,  KCN,  and  potas- 
sium cyanate,  KCNO,  are  produced,  the  process  being  analogous 

340 


§256]  CYANOGEN  AND  HYDROCYANIC  ACID.  341 

to  the  formation  of  potassium  chloride,  KC1,  and  potassium  hypo- 
chlorite,  KC10,  by  the  action  of  chlorine  on  potassium  hydroxide 
("  Inorganic  Chemistry,"  56).  Silver  cyanide,  like  silver  chloride, 
is  in  consistence  a  cheese-like  substance,  insoluble  in  water  and 
dilute  acids,  and  soluble  in  ammonium  hydroxide. 

On  reduction  with  sulphurous  acid,  cyanogen  is  converted 
slowly  into  hydrocyanic  acid,  HCN,  whereas  the  corresponding 
reduction  of  halogens  to  hydrogen  halides  takes  place  instan- 
taneously. 

At  ordinary  temperatures  cyanogen  is  a  gas  of  pungent  odour : 
its  boiling-point  is  —  20  •  7°.  It  is  excessively  poisonous.  At  high 
temperatures  it  is  stable,  but  at  ordinary  temperatures  its  aqueous 
solution  decomposes  slowly,  depositing  a  brown,  amorphou3r 
flocculent  precipitate  of  azulminic  acid.  Cyanogen  is  inflammable^ 
burning  with  a  peach-blossom  coloured  flame. 

Hydrocyanic  Acid,  HCN. 

256.  When  sparks  from  an  induction-coil  are  passed  through  a 
mixture  of  acetylene  and  nitrogen,  hydrocyanic  acid  ("  prussic 
acid  ")  is  formed,  and,  since  acetylene  can  be  obtained  by  direct 
synthesis  (126),  this  reaction  furnishes  a  method  of  building  up 
hydrocyanic  acid  from  its  elements.  Its  synthesis  is  also  effected 
by  electrically  raising  the  temperature  of  a  carbon  rod  to  white 
heat  in  an  atmosphere  of  hydrogen  and  nitrogen,  4*7  per  cent, 
of  hydrocyanic  acid  being  formed  at  2148°.  It  is  usually  pre- 
pared by  heating  potassium  ferrocyanide  (257)  with  dilute  sul- 
phuric acid,  anhydrous  hydrocyanic  acid  being  obtained  by 
fractional  distillation  of  the  aqueous  distillate.  It  is  a  colourless 
liquid  with  an  odour  resembling  that  of  bitter  almonds:  it  boils 
at  26°,  and  the  solid  melts  at  - 14°. 

When  pure,  hydrocyanic  acid  is  stable,  but  its  aqueous  solu- 
tion decomposes  with  formation  of  brown,  amorphous,  insoluble 
substances:  the  solution  contains  various  compounds,  among 
them  ammonium  formate. 

Like  most  cyanogen  derivatives,  hydrocyanic  acid  is  an  exces- 
sively dangerous  poison.  The  inhalation  of  hydrogen  peroxide,  or  of 
air  containing  chlorine,  is  employed  as  an  antidote.  Like  the  mer- 
cury compounds  ("  Inorganic  Chemistry,''  274),  its  toxic  effect  de- 


342  ORGANIC  CHEMISTRY.  [§257 

pends  upon  the  decree  of  ionization,  so  that  it  must  be  the  cyanogen 
ions  that  exert  the  poisonous  action.  Other  evidence  leads  to  the 
same  conclusion-  thus,  potassium  ferrocyanide,  the  aqueous  solution 
of  which  contains  no  cyanogen  ions,  is  non-poisonous. 

Hydrocyanic  acid  must  be  looked  upon  as  the  nitrile  of  formic 
acid:  H-COOH  -» H-CN.  Its  formation  by  the  distillation  of 
ammonium  formate,  and  the  reverse  transformation — referred  to 
above — of  hydrocyanic  acid  into  ammonium  formate  by  addition 
of  two  molecules  of  water,  favour  this  view,  as  does  also  the  forma- 
tion of  hydrocyanic  acid  when  chloroform,  H'CC13,  is  warmed 
with  alcoholic  ammonia  and  caustic  potash-  (145).  Methylamine 
is  obtained  by  reduction  of  hydrocyanic  acid : 

H.C=N+4H  =  H3C-NH2. 

Hydrocyanic  acid  is  one  of  the  weakest  acids,  its  aaueous  solu- 
tion having  low  electric  conductivity. 

Hydrocyanic  acid  can  be  obtained  from  amygdalin,  C2oH27OnN, 
which  is  a  glucoside  (217),  and  is  found  in  bitter  almonds  and  other 
vegetable-products.  In  contact  with  water,  amygdalin  is  decom- 
posed by  an  enzyme  (222),  emulsin,  also  present  in  bitter  almonds, 
into  benzaldehyde,  hydrocyanic  acid,  and  dextrose: 

C,oH,70,,N+2H,0  =  C7H,0+HCN+2C,Hi,06. 

Amygdalin  Benzaldehyde  Dextrose 

Cyanides. 

257.  The  cyanides,  or  salts  of  hydrocyanic  acid,  are  pro- 
duced when  carbon,  nitrogen,  and  a  strong  base  are  in  contact 
at  red  heat;  for  example,  when  a  mixture  of  carbon  and  potassium 
carbonate  is  strongly  heated  in  a  current  of  nitrogen.  Cyanides 
are  also  formed  by  heating  nitrogenous  organic  substances  with 
an  alkali  or  alkali-metal  (4).  Ammonium  cyanide,  NH^N,  is 
obtained  by  passing  ammonia-gas  over  red-hot  carbon. 

When  barium  carbide  is  heated  in  nitrogen,  it  yields  barium 
cyanide : 

BaC2  +  N2  =  Ba(CN)2. 

This  reaction  affords  a  means  of  preparing  cyano-derivatives  from 
atmospheric  nitrogen. 


§257]  CYANIDES.  343 

A  good  yield  of  potassium  cyanide,  KCX,  or  sodium  cyanide, 
XaCX,  is  readily  obtained  by  heating  magnesium  nitride  with 
potassium  or  sodium  carbonate  and  carbon: 


Xa2C03  +  C  =  2XaCX  +  3MgO. 

The  isolation  of  the  nitride  can  be  avoided  by  passing  nitrogen 
over  a  mixture  of  magnesium-powder,  sodium  carbonate,  and 
carbon  at  elevated  temperature  : 

3Mg  +  Xa2CO3  +  C  +  X2  -  2XaCX  +  3MgO. 

The  cyanides  of  the  alkali-metals  and  of  the  alkaline-earth- 
metals,  and  mercuric  cyanide,  are  soluble;  other  cyanides  are  in- 
soluble. All  have  a  great  tendency  to  form  complex  salts,  many 
of  which,  particularly  those  containing  alkali  -metals,  are  soluble 
in  water  and  crystallize  well.  The  preparation  and  properties  of 
some  of  these  salts  are  described  in  "  Inorganic  Chemistry/'  308. 

Potassium  cyanide,  KCX,  is  obtained  by  heating  potassium 
ferrocyanide,  K4Fe(CX)6,  to  redness: 

K4Fe(CX)6  =4KCX  +  FeC2  +  N2. 

Potassium  cyanide  is  readily  soluble  in  water,  and  with  difficulty 
in  strong  alcohol:  it  can  be  fused  without  undergoing  decomposi- 
tion. The  aqueous  solution  is  unstable;  the  potassium  cyanide 
takes  up  t\vo  molecules  of  water,  slowly  at  ordinary  temperatures 
and  quickly  on  boiling,  with  elimination  of  ammonia,  and  produc- 
tion of  potassium  formate: 

KCN+2H20  =  HCOOK+XH3. 

Potassium  cyanide  always  has  an  odour  of  hydrocyanic  acid,  owing 
to  the  fact  that  it  is  decomposed  by  the  carbon  dioxide  of  the 
atmosphere  into  this  compound  and  potassium  carbonate. 

The  aqueous  solution  of  potassium  cyanide  has  a  strongly  alka- 
line reaction,  the  salt  being  partially  hydrolyzed  to  hydrocyanic 
acid  and  caustic  potash  ("Inorganic  Chemistry,"  66).  Evidence 
of  this  decomposition  is  also  afforded  by  the  possibility  of  saponi- 
fying esters  with  a  solution  of  potassium  cyanide,  this  furnishing 
at  the  same  time  a  method  of  determining  the  extent  of  the  hydro- 
lytic  decomposition  of  the  salt. 

Potassiumferrocyanide,'Ki¥e(CN)  6,  crystallizes  in  large,  sulphur- 


344  ORGANIC  CHEMISTRY.  [§258 

yellow  crystals,  with  three  molecules  of  water,  which  can  be  driven 
off  by  the  application  of  gentle  heat,  leaving  a  white  powder.  It  is 
not  poisonous  (256) .  When  warmed  with  dilute  sulphuric  acid  it 
yields  hydrocyanic  acid.  On  heating  with  concentrated  sulphuric 
acid,  carbon  monoxide  is  evolved;  in  presence  of  the  sulphuric 
acid,  the  hydrocyanic  acid  first  formed  takes  up  two  molecules  of 
water,  with  production  of  ammonia  and  formic  acid,  the  latter 
being  immediately  decomposed  by  the  concentrated  sulphuric 
acid  into  carbon  monoxide  and  water  (81).  This  method  is  often 
employed  in  the  preparation  of  carbon  monoxide. 


Cyanic  Acid,  HCNO. 

258.  Cyanic  acid  is  obtained  by  heating  its  polymeride,  cyanuric 
acid  (262),  and  passing  the  resulting  vapours  through  a  freezing- 
mixture.  It  is  a  colourless  liquid,  stable  below  0°.  If  the  flask 
containing  it  is  removed  from  the  freezing-mixture,  so  that  the 
temperature  rises  above  0°,  vigorous  ebullition  takes  place,  some- 
times accompanied  by  loud  reports,  and  the  liquid  is  converted 
into  a  white,  amorphous  solid.  This  transformation  was  first 
observed  by  LIEBIG  and  WOHLER,  by  whom  the  product  was  called 
"insoluble  cyanuric  acid,"  or  cyamelide,  which  is  a  polymeride  of 
cyanic  acid,  and  probably  has  the  formula  (HCNO)3.  It  has, 
however,  been  shown  by  SENIER  that  the  transformation-product 
contains  only  about  30  per  cent,  of  cyamelide,  the  remainder 
being  cyanuric  acid:  they  can  be  separated  by  treatment  with 
water,  in  which  cyamelide  is  very  sparingly  soluble,  much  less 
so  than  cyanuric  acid. 

The  relationship  subsisting  between  cyanic  acid,  cyanuric  acid, 
and  cyamelide  is  explained  by  the  following  considerations.  At 
ordinary  temperatures  cyamelide  is  the  stable  modification.  When 
cooled  below  0°,  the  vapour  of  cyanuric  acid  yields  cyanic  acid,  a 
transformation  analogous  to  the  condensation  of  phosphorus-vapour 
at  low  temperatures  to  the  yellow,  and  not  to  the  stable  red,  modi- 
fication. This  is  due  to  the  fact  that  at  low  temperatures  the  velocity 
of  transformation  of  both  the  unstable  forms  is  very  small.  Above 
0°  the  velocity  of  transformation  of  cyanic  acid  is  much  greater,  and 
the  polymeric,  stable  cyamelide  is  formed,  the  process,  moreover, 
being  considerably  accelerated  by  its  own  calorific  effect.  Above 
150°  cyamelide  is  converted  into  the  isomeric  cyanuric  acid.  This 


§259]  CYANIC  ACID.  345 

transformation  is  analogous  to  that  of  rhombic  sulphur  into  mono- 
clinic  sulphur,  the  transition-point  being  about  150°,  although  the 
process  is  so  slow  that  it  could  not  be  determined  accurately.  A 
similar  slowness  prevents  observation  of  the  reverse  process,  the 
direct  transformation  of  cyanuric  acid  into  cyamelide,  so  that 
cyanuric  acid  remains  unchanged  for  an  indefinite  period  at  the 
ordinary  temperature,  although  it  is  an  unstable  modification.  In 
this  respect  it  is  comparable  with  detonating  gas  ("Inorganic 
Chemistry,"  13). 

Above  0°  an  aqueous  solution  of  cyanic  acid  changes  rapidly 
into  carbon  dioxide  and  ammonia: 

HCNO  +  H20  =  H3N+CO2. 

The  constitution  of  cyanic  acid  itself  is  unknown,  but  it  yields 
two  series  of  derivatives  which  may  be  regarded  as  respectively 

OTT 

derived  from  normal  cyanic  acid,  C^       ,  and  from  isocyanic  acid, 


Cyanogen  chloride,  CNC1,  may  be  looked  upon  as  the  chloride  of 
normal  cyanic  acid.  It  is  a  very  poisonous  liquid,  and  boils  at 
15  '5°:  it  can  be  obtained  by  the  action  of  chlorine  on  hydrocyanic 
acid,  and  polymerizes  readily  to  cyanuric  chloride,  03X3013. 
Cyanogen  chloride  is  converted  by  the  action  of  potassium  hydrox- 
ide into  potassium  chloride  and  potassium  cyanate  : 

CXC1+2KOH  =CXOK  +  KC1  +  H2O. 

259.  Esters  of  cyanic  acid  have  not  been  isolated:  they  are 
probably  formed  in  the  first  instance  by  the  action  of  sodium 
alkoxicles  upon  cyanogen  chloride,  since  the  polymeride,  ethyl 
cyanurate  (CXOC2H5)3,  can  readily  be  separated  from  the  reaction- 
product  (262). 

Esters  of  isocyanic  acid,  on  the  other  hand,  are  well  known,  and 
are  obtained  by  the  action  of  alkyl  halides  on  silver  cyanate: 

CO:N|Ag+I|C2H5  =  CO.NC2H5+AgL 

The  isocyanic  esters  are  volatile  liquids,  with  a  powerful,  stifling 
odour:  they,  too,  polymerize  readily,  yielding  isocyanuric  esters  } 
such  as  (CONC2H5)3  (262). 

The  constitution  of  the  zsocyanic  esters  follows  from  their  decom- 


346 


ORGANIC  CHEMISTRY. 


[§2GO 


position  into  carbon  dioxide  and  an  amine,  by  treatment  with  water, 
or  better  with  dilute  alkalis: 

CO:N.CH3+H2O  =  CO2+NH2.CH3. 

This  reaction  was  first  applied  by  WURTZ  to  the  preparation  of 
primary  amines,  for  obtaining  them  pure,  and  free  from  secondary 
and  tertiary  amines. 

Primary  amines  can  be  obtained  from  acid  amides  by  the  action 
of  bromine  and  caustic  potash  (96).  This  is  more  economically 
effected  by  distilling  a  mixture  of  the  acid  amide  and  bleaching- 
powder  with  lime-water.  The  mechanism  of  the  reaction  has  been 
investigated  by  HOOGEWERFF  and  VAN  DORP.  The  first  product  has 
been  isolated;  it  is  a  substituted  amide,  with  bromine  linked  to 
nitrogen:  R-CO-NH2->R-CO-:NHBr.  The  hydrogen  of  the  ammo- 
group  can  be  replaced  by  metals,  owing  to  the  influence  of  the  acid- 
residue,  and  this  replacement  is  considerably  facilitated  by  the  intro- 
duction of  a  Br-atom.  The  caustic  potash  present  causes  the  forma- 
tion of  a  compound,  R*CO-NKBr,  which  is  unstable,  but  can  be  iso- 
lated. This  potassium  bromoamide  readily  undergoes  an  intra- 
molecular transformation,  similar  to  the  BECKMANN  transformation 
(103): 

R-OOK  Br-C-OK 

changes  to 


Br-N 

Potassium 
b.omoamide 


R-N 


The  transformation-product  loses  KBr,  with  formation  of  an  iso- 

N.R 
cyanic  ester,  ||      ,  which  is  decomposed  by  the  water  present  into 

OC 
a  primary  amine  and  carbon  dioxide. 

Thiocyanic  Acid,  HCNS. 

260.  Thiocyanic  acid  (sulphocyanic  acid)  resembles  cyanic  acid 
in  its  properties,  but  is  much  more  stable  towards  water.  It  can 
be  obtained  by  treatment  of  barium  thiocyanate  with  the  calculated 
proportion  of  dilute  sulphuric  acid.  The  anhydrous  acid  is 
obtained  by  the  action  at  low  temperature  of  concentrated  sul- 
phuric acid  on  a  mixture  of  potassium  thiocyanate  and  phosphoric 
oxide,  the  oxide  being  added  to  prevent  excess  of  moisture.  At  0° 
it  forms  a  white,  crystalline  solid,  melting  at  about  5°,  and  quickly 
changing  to  a  solid  polymeride  after  removal  from  the  freezing- 


§  260]  THJOCYANIC  ACID.  347 

mixture.  When  warmed  with  dilute  sulphuric  acid,  thiocyanic 
acid  takes  up  one  molecule  of  water,  and  decomposes  similarly 
to  cyanic  acid  (258),  with  production  of  carbon  oxysulphide, 
COS,  instead  of  carbon  dioxide: 

HCNS+H2O   =  HsN+COS. 

Potassium  thiocyanate  is  obtained  by  boiling  a  solution  of  potas- 
sium cyanide  with  sulphur.  Among  other  applications  it  is  used  in 
VOLHARD'S  method  of  silver-titration.  When  silver  nitrate  is  added 
to  a  solution  of  potassium  thiocyanate,  silver  thiocyanate,  AgCNS,  is 
deposited  in  the  form  of  a  white,  cheese-like  precipitate,  insoluble  in 
dilute  mineral  acids.  Ferric  thiocyanate,  Fe(CNS)3,  has  a  dark 
blood-red  colour :  its  formation  is  used  as  a  test  for  ferric  salts.  The 
red  colour  is  due  to  the  non-ionized  molecules  Fe(CXS)3,  since  neither 
the  ferric  ion  nor  the  thiocyanic  ion  are  coloured  in  solution,  and  the 
colour  is  intensified  if  ionization  is  diminished;  for  example,  by  the 
addition  of  more  of  the  ferric  salt  or  of  the  thiocyanate.  The  red 
colour  is  removed  by  agitating  the  solution  with  ether,  whereas  ions 
cannot  be  extracted  by  this  means.  Mercury  thiocyanate  has  the 
property  of  intumescing  when  decomposed  by  heat  ("Pharaoh's 
serpents  "). 

The  constitution  of  thiocyanic  acid,  like  that  of  cyanic  acid,  is 
unknown,  and  it  resembles  the  latter  hi  giving  rise  to  two  series  of 

S«  R 

esters,  the  thiocyanic  esters,  C^r*    ,  and  the  isothiocyanic  esters, 


Thiocyanic  esters  are  obtained  by  the  action  of  alkyl  iodides 
upon  the  salts  of  thiocyanic  acid : 


CN*S|K  +  I|C2H5  =  CN.SC2H5+KI. 

They  are  liquids,  insoluble  hi  water,  and  characterized  by  a  leek- 
like  odour.  That  the  alkyl-group  in  these  compounds  is  in  union 
with  sulphur  is  proved  by  the  nature  of  the  products  obtained  both 
by  reduction  and  oxidation.  Reduction  yields  mercaptans  and 
hydrocyanic  acid,  methylamine  being  formed  from  the  latter  by 
further  reduction : 

CN.S.C2H5+2H  =  CNH+H.S.C2H5. 

Alkylsulphonic  acids,  such  as  C2H5-SO2OH  (60),  are  obtained  by 
oxidation. 


348  ORGANIC  CHEMISTRY.  [§  260 

Under  the  influence  of  heat  the  thiocyanic  esters  are  trans- 
formed into  i'sothiocyanic  esters:  thus,  distillation  of  allyl  thio- 
cyanate,  CN'SCsHs,  effects  this  change. 

The  ^sothiocyanic  esters  are  also  called  mustard-oils,  after  allyl 
isothiocyanate,  to  which  the  odour  and  taste  of  mustard-seeds 
are  due.  The  following  reactions  prove  that  these  compounds 
contain  an  alkyl-group  attached  to  nitrogen,  and  have  the  con- 

XN-R 
stitution  CC         .     When  treated  with  concentrated  sulphuric  acid, 

they  take  up  water,  yielding  a  primary  amine  and  carbon  oxy- 
sulphide : 

R-N:CS+H2O  =  R-NH2+COS. 

They  are  converted  by  reduction  into  a  primary  amine  and  trithio- 
methylene,  (CH2S)3,  the  latter  probably  resulting  from  the  polymeri- 
zation of  the  thiomethylene,  CH2S,  first  formed,  which  is  unknown 
in  the  free  state: 

R-N:CS+4H  =  R.NH2+CH2S. 

Addition-products  of  the  mustard-oils  are  described  in  269  and  270. 

Cyanamide,  CN-NH2,  is  obtained  in  various  reactions;  for  in- 
stance, by  the  action  of  ammonia  upon  cyanogen  chloride.  It  is  a 
crystalline,  hygroscopic  solid,  and  polymerizes  readily.  Its  hydro- 
gen atoms  can  be  replaced  by  metals;  thus,  silver  yields  silver 
cyanamide,  CN-NAg2,  which  is  yellow,  and  insoluble  in  dilute 
ammonium  hydroxide,  wherein  it  differs  from  most  silver  com- 
pounds. 

When  calcium  carbide  is  heated  to  redness  in  a  current  of 
nitrogen,  calcium  cyanamide  is  formed : 

CaC2  +  N2  =  CN-NCa  +  C. 

The  absorption  of  nitrogen  is  much  facilitated  by  addition  of 
10  per  cent,  of  calcium  chloride :  This]  compound  can  also  be 
obtained  by  heating  lime  and  carbon  to  a  red  heat  in  an  atmos- 
phere of  nitrogen.  The  crude  product  is  called  "  Lime-nitrogen  " 
(German,  Kalkstickstoff),and  finds  application  as  an  artificial 
fertilizer,  being  decomposed  slowly  by  water  at  ordinary  tempera- 
tures into  ammonia  and  calcium  carbonate; 

CaCN2+3H20  =  2NH3+CaCO3. 


§§261,262]  FULMINIC   ACID.  349 

The  reaction  is  much  accelerated  by  heating  under  pressure. 
Ammonia  can  be  obtained  directly  from  the  nitrogen  of  the  at- 
mosphere by  this  method. 

Fulminic  Acid. 

261.  Salts  of  fulminic  acid  are  obtained  by  the  interaction  of 
mercury  or  silver,  nitric  acid,  and  alcohol,  in  certain  proportions* 
The  best  known  of  them  is  mercuric  fulminate,  HgC2O2N2,  which  is 
prepared  on  a  large  scale,  and  employed  for  filling  percussion-caps, 
and  for  other  purposes.  .Guncotton  can  be  exploded  by  the  detona- 
tion of  a  small  quantity  of  this  substance  (228) ;  and  it  produces  the 
same  result  with  other  explosives,  so  that  the  so-called  "fulminating 
mercury  "  plays  an  important  part  in  their  application. 

Silver  fulminate,  Ag(CNO),  is  much  more  explosive  than  the  mer- 
cury salt,  and  hence  is  not  employed  technically.  The  explosion  of 
these  salts  has  a  bn'sant  (155),  though  only  local,  effect:  this  enabled 
HOWARD,  the  discoverer  of  mercuric  fulminate,  to  explode  a  small 
quantity  in  a  balloon  without  injury  to  the  latter,  the  only  effect 
being  to  shatter  the  leaden  shells  containing  the  explosive. 

Free  fulminic  acid  is  a  very  unstable,  volatile  substance :  it  has 
an  odour  resembling  that  of  hydrocyanic  acid,  and  is  excessively 
poisonous. 

According  to  NEF,  the  formula  of  fulminic  acid  is  C=X«OH,  con- 
taining a  bivalent  carbon  atom.  When  mercuric  fulminate  is  treated 
with  acetyl  chloride,  a  compound  of  the  formula  CH3-CO(CXO)  is 
obtained.  In  presence  of  hydrochloric  acid  the  fulminate  takes  up 
water,  with  formation  of  hydroxylamine  and  formic  acid.  It  is  con- 
verted by  bromine  into  a  compound,  Br2C2O2N2,  with  the  constitu- 
tional formula 

Br— C=N— O 

Br— C=N— O* 

Cyanuric  Acid  and  z'soCyanuric  Acid. 

262.  Cyanuric  bromide,  C3N3Br3,  is  obtained  by  heating  potas- 
sium ferricyanide  with  bromine  at  220°.  By  heating  with  water, 
the  bromide  is  converted  into  cyanuric  acid,  (CNOH)3.  The  latter, 
however,  is  usually  prepared  by  the  action  of  heat  on  urea  (267). 
Two  series  of  esters  are  derived  from  this  acid,  the  normal  cyanuric 
and  the  isocyanuric  esters,  the  former  being  called  "Q-esters,"  and 
the  latter  "N-esters." 


350  ORGANIC  CHEMISTRY.  [§  262 

The  normal  cyanuric  esters  are  obtained  by  the  action  of  sodium 
alkoxides  on  cyanuric  chloride  or  bromide.  The  formation  of  alco- 
hol and  cyanuric  acid  on  saponification  proves  the  alkyl-group  in 
these  esters  to  be  in  union  with  oxygen.  For  this  reason  constitu- 
tional formula  I.  is  assigned  to  them: 

N  N.R  o 


/\ 

RO-C      C-OR  OC      CO  HN:C      C:NH 

I     II       ;  II  I 

N     X  R-N     N-R  O 


O 


c  co  C:NH 

OR 
I.  II.  III. 

The  isocyanuric  esters  result  when  silver  cyanurate  is  heated 
with  an  alkyl  iodide.  Their  alkyl-groups.  are  linked  to  nitrogen, 
since,  on  boiling  with  alkali,  such  an  ester  yields  a  primary  amine 
and  carbon  dioxide,  a  decomposition  accounted  for  in  constitutional 
formula  II.  The  O-esters  are  formed  when  an  alkyl  iodide  reacts 
with  silver  cyanurate  at  ordinary  temperatures,  but  their  conver- 
sion into  the  N-esters  by  heating  explains  the  difference  in  the 
products  obtained  at  ordinary  and  at  elevated  temperatures. 

KLASON  has  suggested  that  cyamelide  (258)  is  isocyanuric  acid, 
and  that  its  relation  to  the  isocyanuric  esters  resembles  that  of 
cyanuric  acid  to  the  normal  cyanuric  esters.  The  formation  of 
cyanuric  chloride  by  the  action  of  phosphorus  pentachloride  on 
the  normal  esters  and  normal  cyanuric  acid,  and  the  fact  that  the 
iso-esters,  and,  as  SENIER  has  shown,  cyamelide,  do  not  yield  chlo- 
rides under  this  treatment,  support  this  view. 

Important  evidence  in  favour  of  the  imino-formula  for  cyanuric 
acid  has  been  furnished  by  CHATTAWAY  and  WADMORE,  who  have 
succeeded  in  replacing  the  metal  in  potassium  cyanurate  by 
chlorine.  They  regard  the  compound  formed  as  (O:C:N»C1)3. 

Formula  III.,  containing  imino-groups,  possibly  represents 
the  structure  of  cyamelide. 


DERIVATIVES  OF  CARBONIC  ACID.] 
263.  Carbonic  acid,  H2C03  or  CO(OH)2,  is  not  known  in  the 
free  state,  but  is  supposed  to  exist  in  the  solution  of  carbon  dioxide 
in  water:  it  decomposes  very  readily  into  its  anhydride,  carbon 
dioxide,  and  water.  It  is  dibasic,  and  is  generally  described,  with 
its  salts,  in  inorganic  chemistry  ("Inorganic  Chemistry/'  184). 
Some  of  its  organic  derivatives  are  dealt  with  in  this  chapter. 

Carbonyl  Chloride,  COC12 

Carbonyl   chloride    (phosgene)    is   prepared    by   heating   chlo- 
rine and  carbon  monoxide;  an  equilibrium 

C12  +  CO<=±COC12, 

is  attained,  corresponding  at  505°  with  about  67  per 
cent,  of  dissociation.  It  was  called  phosgene  (<£o>s,  light; 
yewdu,  to  produce)  by  J.  DAVY  in  1811,  under  the  impression 
that  its  formation  by  this  means  can  only  take  place  in  presence  of 
sunlight,  a  view  since  proved  to  be  incorrect.  Carbonyl  chloride  is 
a  gas  with  a  powerful,  stifling  odour.  It  dissolves  readily  in  benzene, 
and  the  solution  is  employed  in  syntheses,  both  in  the  laboratory 
and  in  the  arts. 

At  ordinary  temperature,  carbonyl  chloride  is  decomposed  by 
ultraviolet  light,  especially  by  the  rays  of  short  wave-length,  into 
carbon  monoxide  and  chlorine,  the  mechanism  of  the  process  being 
similar  to  that  described  in  "Inorganic  Chemistry,"  79.  Carbon 
monoxide  and  chlorine  also  combine  under  the  influence  of  this 
light,  so  that  an  equilibrium  is  established. 

The  reactions  of  carbonyl  chloride  indicate  that  it  is  the  chloride 
of  carbonic  acid.  It  is  slowly  decomposed  by  water,  yielding  hydro- 
chloric acid  and  carbon  dioxide.  With  alcohol  at  ordinary  tem- 
peratures it  first  forms  ethyl  chlorocarbonate; 


CO      + 


X)C2H5 
CO 


By  more  prolonged  treatment  with  alcohol,  and  also  by  the  action 
of  sodium  ethoxide,  diethyl  carbonate,  CO(OC2H5)2,  is  produced. 
By  the  action  of  ammonia,  the  two  Cl-atoms  in  carbonyl  chloride 
can  be  replaced  by  amino-groups,  with  formation  of  the  amide  of 

351 


352  ORGANIC  CHEMISTRY  [§  264 

carbonic  acid,  urea,  CO(NH2)2  (266).  All  these  reactions  are 
characteristic  of  acid  chlorides. 

The  ehlorocarbonic  esters,  also  called  chloroformic  esters,  are  col- 
ourless liquids  of  strong  odour,  and  distil  without  decomposition. 
They  are  employed  for  the  introduction  of  the  group  — COOC2H5 
into  compounds  (235). 

The  carbonic  esters  are  also  liquids,  but  are  characterized  by  the 
possession  of  an  ethereal  odour :  they  are  insoluble  in  water,  and  are 
very  readily  saponified. 

Carbon  Bisulphide,  CS2. 

264.  Carbon  disulphide  is  manufactured  synthetically  by  passing 
sulphur- vapour  over  red-hot  carbon.  The  crude  product  has  a  very 
disagreeable  odour,  which  can  be  removed  by  distilling  from  fat. 
The  pure  product  is  an  almost  colourless,  highly  refractive  liquid 
of  ethereal  odour.  It  is  insoluble  in  water,  boils  at  46°,  and  has  a 
specific  gravity  of  1-262  at  20°.  Carbon  disulphide  is  poisonous: 
being  highly  inflammable,  it  must  be  handled  with  great  care.  It 
is  an  excellent  solvent  for  fats  and  oils,  and  finds  extensive  applica- 
tion in  the  extraction  of  these  from  seeds.  It  is  also  employed  in 
the  vulcanization  of  india-rubber. 

Carbon  disulphide  is  a  stable  compound,  and  resists  the  action 
of  heat,  although  it  is  endothermic  ("  Inorganic  Chemistry,"  119). 
It  is,  however,  possible  to  make  its  vapour  explode  by  means  of 
mercuric  fulminate.  The  halogens  have  little  action  on  it  at  ordi- 
nary temperatures;  but  in  presence  of  a  halogen-carrier,  chlorine  and 
bromine  can  effect  substitution,  with  production  of  carbon  tetra- 
chloride  and  tetrabromide  respectively. 

Carbon  disulphide,  like  carbon  dioxide,  is  the  anhydride  of  an 
acid,  or  an  anhydrosulphide.  With  alkali-metal  or  alkaline-earth- 
metal  sulphides  it  yields  trithiocarbonates: 

BaS+CS2  =  BaCS3. 

Barium 
trithiocarbonate 

The  barium  salt  is  yellow,  and  dissolves  in  cold  water  with  difficulty. 
By  the  addition  of  dilute  acids  to  its  salts,  free  trithiocarbonic  acid, 
H2CSs,  can  be  obtained  as  an  unstable  oil.  The  potassium  salt  is 
employed  in  the  destruction  of  vine-lice. 


§§  265,  266]    XANTHIC  ACID  AND  CARBON  OXY  SULPHIDE.         353 

The  potassium  salt  of  xanthic  acid  is  formed  by  the  action  of 
potassium  ethoxide  on  carbon  disulphide: 

/OC2Hs 
CS2  +  KOC2H5  =  CS 

\SK 

This  is  effected  by  agitating  carbon  disulphide  with  a  solution  of 
caustic  potash  in  absolute  alcohol,  when  potassium  xanthate  sepa- 
rates in  the  form  of  yellow,  glittering  needles.  Free  xanthic  acid 
is  very  unstable:  it  owes  its  name  (£av66s.  yellow)  to  its  cuprous 
salt,  which  has  a  yellow  colour,  and  results  from  the  spontaneous 
transformation  of  the  brownish-black  cupric  salt,  precipitated  from 
a  solution  of  copper  sulphate  by  the  addition  of  a  xanthate. 

Carbon  Oxysulphide,  COS. 

265.  Carbon  oxysulphide  is  a  colourless,  odourless,  inflammable 
gas,  and  is  obtained  by  the  action  of  sulphuretted  hydrogen  on 
isocyanic  esters: 

2CO.NC2H5+H2S  =  COS+CO(NHC2H5)2. 

Its  formation  from  tsothiocyanic  esters  is  mentioned  in  260.  It  is 
also  produced  when  a  mixture  of  carbon  monoxide  and  sulphur- 
.vapour  is  passed  through  a  tube  at  a  moderate  heat. 

Carbon  oxysulphide  is  but  slowly  absorbed  by  alkalis.  It  yields 
salts  with  metallic  alkoxides:  these  compounds  may  be  regarded 
as  derived  from  carbonates  by  simultaneous  exchange  of  oxygen  for 
sulphur: 

xOC2Hs 
COS+C2H5.OK  =  CO 


266.  Urea  owes  its  name  to  its  occurrence  in  urine,  as  the  final 
decomposition-product  of  the  proteins  in  the  body. 

An  adult  excretes  about  1500  grammes  of  urine,  containing  ap- 
proximately 2  per  cent,  of  urea,  in  twenty-four  hours,  so  that  the 
daily  production  of  this  substance  amounts  to  about  30  grammes. 


3")i  ORGANIC  CHEMISTRY.  [§266 

To  obtain  urea  from  urine,  the  latter  is  first  concentrated  by  evapora- 
tion. On  addition  of  nitric  acid,  urea  nitrate,  %CO(NH2)2-HN03, 
(267)  is  precipitated,  and,  on  account  of  impurities,  has  a  yellow 
colour.  The  colouring  is  removed  by  dissolving  the  precipitate  in 
water,  and  oxidizing  with  potassium  permanganate.  Urea  is  set 
fres  from  the  solution  of  the  nitrate  by  treatment  with  barium 
carbonate  : 

2CON2H4-HNO3+BaCO3  =  2CON2H4+Ba(NO3)2  +  H20+CO2. 

Urea  nitrate 

On  evaporation  to  dryness,  a  mixture  of  urea  and  barium  nitrate  is 
obtained  from  which  the  organic  compound  can  be  separated  by 
solution  in  strong  alcohol. 

Urea  is  to  be  looked  on  as  the  amide  of  carbonic  acid,  on  account 
of  its  formation,  along  with  cyanuric  acid  and  cyamelide,  from 
the  chloride  of  this  acid,  carbonyl  chloride,  COC12,  this  reaction 
proving  its  constitution  (263)  : 

H|NH2      / 

=  CO         +2HC1. 
HNH2      \NH2 

Urea 

A  confirmation  of  this  view  of  the  constitution  of  urea  is  its  forma- 
tion by  the  action  of  ammonia  on  diethyl  carbonate. 

Urea  is  formed  by  addition  of  ammonia  to  isocyanic  acid: 

NH  /NH2 

+NH3  =  CO        . 


Anmoniu  n  {socyanate  dissolved  in  water  is  transformed  into  urea 
on  evaporation  of  the  solution.  This  is  the  method  by  which 
WOHLES  ejected  his  classic  synthesis  of  urea,  by  heating  a  mixture 
of  potassium  cyanate  and  ammonium  sulphate  in  solution  (i). 

This  reaction,  which  has  an  important  bearing  upon  the  history 
of  organic  chemistry,  has  been  studied  in  detail  by  JAMES  WALKER 
and  HAMBLY.  Their  researches  have  shown  that  the  reverse  trans- 
formation of  urea  into  ammonium  isocyanate  occurs  also,  since,  on 
addition  of  silver  nitrate,  a  solution  of  pure  urea  in  boiling  water 
yields  a  precipitate  of  silver  cyanate.  An  equilibrium  is  attained: 

CO(NH2)2^CON-NH4. 

TT  Ammonium 

Urea  tsocyanate 


§26?]  UREA.  -  355 

When  this  equilibrium  is  reached,  the  solution  only  contains  a  small 
percentage  of  i^anate.  It  is  almost  independent  of  the  tempera- 
ture, proving  that  the  transformation  of  the  systems  into  one  another 
is  accompanied  by  but  slight  calorific  effect  (94). 

;    woCyanic  esters  are  decomposed  by  water,   with  formation 
f  primary  amines  and  carbon  dioxide   (259).     If  the  primary 
amme  formed  is  brought  into  contact  with  a  second  molecule  of 
wocyamc    ester,    addition    takes    place,    with    production    of    ; 
sij  m  metrical  dialkyl-urea: 


/NHR 
CO:NR+H2NR'  =  CO 


This  is  a  general  method  for  preparing  symmetrical  dialkylureas. 

A  monoalkylurea  is  obtained  by  the  action  of  ammonia,  instead  of 
an  amme,  upon  an  zsocyanic  ester. 


/NRR' 


Unsymmetrical  dialkylureas,  CO  ,  are  prepared  by  the  action 

XNH2 

of  wocyanic  acid  on  secondary  amines.     The  method  of  procedure  is 
analogous  to  that  employed  in  WOHLER'S  synthesis  of  urea,  and  con- 

i  m  warming  a  solution  of  the  wocyanate  of  a  secondary  amine: 


CONH-NHRR' 


The  unsymmetrical  dialkylureas  are  converted  by  treatment  with 
Dlute  (100  per  cent.)  nitric  acid  into  nitro-compounds,  which  were 
discovered  by  FRANCHIMONT,  and  are  called  mtroamines' 


(CH3)2N 


COXH. 


+NO2-|OH 


267.  Urea    crystallizes    in     elongated     prisms,    the    crystals 
esemblmg  those   of  potassium  nitrate.     They  are  very  soluble 
MI    water     and    melt    at    132°.     Like    the    amines,    urea    forms 
by  addition  of  acids,  but  only  one  NH2-group  can  react  thus 
these   salts    the    nitrate,    CO.\2H4,HNO3,   and    the   oxalate 


356  ORGANIC  CHEMISTRY.  [§  267 


4,   dissolve   with   difficulty  in   solutions   of    the 
corresponding  acids. 

In  some  of  its  reactions,  notably  in  certain  condensation-pro- 

XNH 
cesses,  urea  behaves  as  though  it  had  the  structure  C  —  OH.    An 

^Nfla 

ether  of  this  isourea  is  obtained  by  addition  of  methyl  alcohol  to 
cyanamide,  the  reaction  being  facilitated  by  the  presence  of  hydro- 
chloric acid: 

XOCH3 


C 

Cyanamide  Methylisourea 

This  method  of  formation  indicates  the  constitution  of  the  com- 
pound. Another  reaction  confirming  this  view  is  the  production  of 
methyl  chloride  on  heating  with  hydrochloric  acid,  which  points  to 
the  fact  that  the  CH3-group  is  not  in  union  with  nitrogen,  since  under 


this    treatment    methylurea,  CO  ,    splits    off    methylamine, 

^NHCHg       - 
CH3-NH2. 

When  heated,  urea  melts;  it  then  begins  to  evolve  a  gas,  con- 
sisting principally  of  ammonia,  but  also  containing  carbon  dioxide; 
after  a  time  the  residue  solidifies.  The  following  reactions  take 
place. 

Two  molecules  of  urea  lose  one  molecule  of  ammonia,  with  pro- 
duction of  biuret: 

/NH2      H2NV 
CO.  _          >CO  =  NH2.CO-NH.CO.NH2+NH3. 

\[NH2H|        X  Biuret 


Biuret  is  a  crystalline  substance  which  melts  at  190°.  When 
copper  sulphate  and  caustic  potash  are  added  to  its  aqueous  solu- 
tion, it  gives  a  characteristic  red  to  violet  coloration  (u  biuret- 
reaction"). 


§267]  UREA.  357 

On  further  heating,  biuret  unites  with  a  molecule  of  unaltered 
urea  with,  elimination  of  ammonia,  and  formation  of  cyanuric 
acid  (262) : 

NH 

CO 

+  2NH3. 


Like  the  acid  amides,  when  heated  with  bases  urea  decomposes, 
yielding  carbon  dioxide  and  ammonia. 

The  quantitative  estimation  of  urea  in  urine  is  an  operation  of 
considerable  importance  in  physiological  chemistry,  and  is  effected 
by  different  methods.  BUNSEN'S  process  depends  upon  the  decom- 
position of  urea  into  carbon  dioxide  and  ammonia,  on  heating  with 
an  ammoniacal  solution  of  baryta:  the  carbon  dioxide  is  thus  con- 
verted into  barium  carbonate,  which  can  be  collected  and  weighed. 
In  KNOP'S  method  the  nitrogen  is  quantitatively  liberated  by  treat- 
ment of  the  urea  solution  with  one  of  caustic  potash  and  bromine 
(German,  Bromlauge),  in  which  potassium  hypobromite  is  present: 
the  percentage  of  urea  can  be  calculated  from  the  volume  of  nitrogen 
liberated.  LIEBIG'S  titration-method  is  based  upon  the  formation 
of  a  white  precipitate  of  the  composition  2CON2H4-  Hg(N03)2-3HgO, 
when  mercuric-nitrate  solution  is  run  into  a  solution  of  urea  of  about 
2  per  cent,  concentration.  When  excess  of  the  mercury  salt  has  been 
added,  a  drop  of  the  liquid  brought  into  contact  with  a  solution  of 
sodium  carbonate  gives  a  yellow  precipitate  of  basic  nitrate  of  mer- 
cury. Urine,  however,  contains  substances  which  interfere  with 
these  methods  of  estimation:  an  account  of  the  mode  of  procedure 
by  which  the  correct  percentage  of  urea  can  be  ascertained  will  be 
found  in  text-books  of  physiological  chemistry. 


Potassium  cyanate  and  hydrazine  hydrate,  H2N 
react  together,  with  formation  of  semicarbazide,  NH2'CO*NH'NH2, 
a  base  which  melts  at  96°,  and  combines  with  aldehydes  and  ketones 
similarly  to  hydroxylamine: 

R2-C|0  +  H2|N-NH.CO-NH2  -»  Ra.C:N-NH-CO-NH2. 

The  compounds  thus  formed  are  called  semicarbazones  ;  they  some- 
times crystallize  well,  and  are  employed  in  the  identification  and 
separation  of  aldehydes  and  ketones. 


358  ORGANIC    CHEMISTRY.  [§238 

Derivatives  of  Carbamic  Acid. 

268.  Carbamic  acid,  NH2-CO»OH,  which  is  the  semi-amide  of 
carbonic  acid,  is  not  known  in  the  free  state,  but  only  as  salts, 
esters,  and  chloride.  Ammonium  carbamate  is  formed  by  the  union 
of  dry  carbon  dioxide  with  dry  ammonia: 

/OH  /OHNH3 


\NH2  \NH2 

Ammonium  carbamate 

When  carbon  dioxide  is  passed  into  an  ammoniacal  solution  of 
calcium  chloride,  no  precipitate  results,  since  the  resulting  calcium 

/Oca* 

carbamate,  CO         ,  is  soluble  in  water. 
\NH2 

When  the  salts  of  carbamic  acid  are  heated  in  solution,  they 
readily  take  up  water,  forming  carbonates. 

The  esters  of  carbamic  acid  are  called  urethanes.  They  are 
formed  by  the  action  of  ammonia  or  amines  upon  the  esters  of 
carbonic  acid  or  chlorocarbonic  acid: 


X!OC2H5  +  HNH2       /NH2 
CO  =  CO  +C2H5OH; 


Diethyl  carbonate  Urethane 

X|C1+H|NH2        /NH2 
CO"  -*CO 

\OC2H5  \OC2H5 

Ethyl  chlorocarbonate 

Urethanes  also  result    in  the   action  of  alcohol  upon  isocyanic 
esters  : 

//O  /OC2H5 

Of  +HOC2H5  =  C=0 

^NCH3  \NHCH3 

Urethanes  are  also  obtained  by  boiling  acid  azides(p7)  with  alcohol: 
R.CON3  +  C2H5OH  =  R-NHCOOC2H5  +  N2 

*  ca  =   Ca. 


269]  URETHANES  AND   THIOUREA.  359 

Since  the  azides  are  easily  prepared  from  the  corresponding  acids, 
and  the  urethanes  readily  yield  the  corresponding  amines,  the  car- 
boxyl-group  can  be  replaced  by  the  amino-group : 

R-COOH  ->  R-COOC2H5  -»  R-COXHXH,  -»  R.CON3  -> 

Acid  Ester  Hydrazide  Azide 

-»R.NHCOOC2H5-+R-XH2. 

Urethane  Primary 


Urethanes  distil   without   decomposition:    ordinary  urethane, 

/OC2H5 
CO  ,  melts  at  51°,  and  is  very  readily  soluble  in  water.     When 

\NH2 

boiled  with  bases,  it  decomposes  into  alcohol,  carbon  dioxide,  and 
ammonia.  Concentrated  nitric  acid  converts  it  into  nitrourethane, 
C2H5O'CO'NH-NO2;  and  on  careful  hydrolysis  this  substance 
yields  nitroamine,  NH2  •  N02. 

Thiourca,  CS(NH2)2. 

269.  Ammonium  tsothiocyanate  yields  thiourea  in  a  manner  analo- 
gous to  the  formation  of  urea  from  ammonium  tsocyanate  (266). 
The  transformation  of  the  thio-compound  can  in  this  instance  be 
effected  by  heating  it  in  the  dry  state,  but  is  no  more  complete  than 
that  of  ammonium  cyanate,  since  thiourea  is  converted  by  heat  into 
ammonium  tsothiocyanate.  Alkyl-derivatives  of  thiourea  result 
from  addition  of  ammonia  or  amines  to  the  mustard-oils  (260)  the 
reaction  being  similar  to  the  formation  of  alkyl-substituted  ureas 
from  isocyanic  esters  (266). 

These  modes  of  formation  prove  that  the  constitution  of  thiourea 
is  expressed  by  the  formula  CS(XH2)2,  being  similar  to  that  of  urea. 
Derivatives  of  thiourea  are  known,  however,  which  point  to  the 

XNH2 
existence  of  a  tautomeric  form  C^-SH      (267)-  thus,  on  addition  of 

^NH 

an  alkyl  iodide,  compounds  are  obtained  in  accordance  with  the 
equation 

NH2 

1^      O  I  TT 


C<-S|H    +     I|C2H5  =    C^SC2H5  JHI. 


The  alkyl-group  in  this  compound  is  linked  to  sulphur;  for  it  de- 
composes with  formation  of  mercaptan,  and  on  oxidation  yields  a 
sulphonic  acid. 


360  ORGANIC  CHEMISTRY.  [§270 

Thiourea  forms  well-defined  crystals,  melting  at  172°,  and  readily 
soluble  in  water,  but  with  difficulty  in  alcohol.  On  treatment  with 
mercuric  oxide,  it  loses  sulphuretted  hydrogen,  forming  cyanamide: 

XN_[H~2          ,N 
p  ic          __  r*/ 

\NHa 

Guanidine, 

270.  Guanidine  is  formed  by  the  interaction  of  ammonia 
and  orthocarbonic  esters  or  chloropicrin,  CC13N02.  This  prob- 
ably results  from  addition  of  four  amino-groups  to  the  carbon 
atom,  the  compound  formed  then  losing  one  molecule  of  am- 
monia: 

/NH2 
C(OC2H5)4  -»  C(NH2)4;  -  NH3  -»  C^NH  . 

Tetraethyl  ortho-  \NHo 

carbonate 

Guanidine 

This  method  of  preparing  guanidine  establishes  the  constitutional 
formula  indicated.  Further  evidence  is  afforded  by  its  synthesis  by 
heating  cyanamide  with  an  alcoholic  solution  of  ammonium  chloride: 

/^  I  /NH2\ 

+NH4C1  =  I  C=NH    HC1. 
V  \NH2/ 

Guanidine  is  generally  prepared  by  heating  ammonium  thiocyanate 
for  six  hours  at  temperatures  rising  from  180°  to  205°,  air  being 
blown  through  the  melt  to  oxidize  the  evolved  sulphuretted 
hydrogen  to  sulphur  and  water,  and  thus  obviate  the  formation 
of  secondary  products: 

2S :  C :  NH  •  NH3  =  H2S  +  (CH5N3)  HCNS. 

It  is  obtained  in  the  form  of  guanidine  thiocyanate,  the  reaction 
taking  place  in  the  following  stages: 

SCNH.NH3-^CS(NH2)2-^H2N.CN. 

Ammonium  thiocyanate       Thiourea  Cyanamide 


§  270]  GUANIDINE  DERIVATIVES  361 

The  cyanamide  unites  with  a  molecule  of  the  unaltered  ammonium 
thiocyanate: 


+  NH3-HCNS  =     C=NH     HCNS. 
NH2  V  \NHj. 

Guanidine  thiocyanate 

Guanidine  is  a  colourless,  crystalline  substance,  and  readily 
absorbs  moisture  and  carbon  dioxide  from  the  atmosphere.  It  is 
a  strong  base,  unlike  urea,  which  has  a  neutral  reaction:  the 
strengthening  of  the  basic  character,  occasioned  by  exchange  of 
carbonyl-oxygen  for  an  imino-group,  is  worthy  of  notice.  Guani- 
dine yields  many  well-defined,  crystalline  salts. 
/NH-NO2 

Nitroguanidine,  C=NH          ,   is  obtained   in   solution   by   the 

\NH2 

action  of  fuming  nitric  acid  upon  guanidine:  dilution  with  water 
precipitates  the  nitroguanidine,  which  is  very  slightly  soluble  in 

/NH-NH2 
water.    On  reduction,  it  yields  aminoguanidine,  C=NH          ,  which, 

\NH2 

on  boiling  with  dilute  acids  or  alkalis,  decomposes  with  formation 
of  carbon  dioxide,  ammonia,  and  diamide  or  hydrazine,  H2N-NH2 
(" Inorganic  Chemistry/7  114).  This  reaction  proves  the  consti- 
tution of  nitroguanidine  and  aminoguanidine. 

An  important  derivative  of  guanidine  is  arginine,  CeH^O^^ 
obtained  from  proteins.  It  can  be  synthesized  by  the  action  of 
cyanamide  on  ornithinc  (243) : 

COOH.CH(NH2).(CH2)3.NH2+CN2H2  = 

Ornithine  Cyanamide 

COOH  -  CHNH2 .  (CH2)3NH 


Arginine 


NH 


The  cyanamide  is   added  at  the  <5-NH2-group,  as   represented  in, 
the  equation,  so  that  arginine  is  a-amino-d-guanino-n-valeric  acid. 


URIC-ACID   GROUP. 

271.  Uric  acid,  C5H403N4,  derives  its  name  from  its  presence 
in  small  amount  in  urine:  it  is  the  nucleus  of  an  important  group 
of  urea  derivatives.  It  is  closely  related  to  the  ureulo-acids  and  the 
acid-ureides  (ureides),  which  are  amino-acids  and  acid  amides,  con- 
taining the  urea-residue,  NH2'CO«NH  —  ,  instead  of  the  NH2-group. 

Parabanic  acid,  C3H2"O3N2,  is  an  acid-ureide:  it  is  obtained  by 
the  oxidation  of  uric  acid.  AVhen  warmed  with  alkalis  for  a  long 
time,  parabanic  acid  takes  up  two  molecules  of  water,  forming  urea 
and  oxalic  acid,  a  reaction  which  proves  it  to  be  oxalylurea: 


x  OHH 


CO  \  COOH 

NCO+      =  i        +      >co. 

CO    /  COOH    rr^f 

\ 

Parabanic  acid  (Oxalylurea) 


H2N 
NH        OHH 


On  careful  treatment  with  alkalis,  it  takes  up  only  one  molecule  of 
water,  yielding  oxaluric  acid: 


CO  CO—  NH  •  CO  •  NH2 

I       /co  -  | 

CO    /  COOH 

Oxaluric  acid 


+OHH 

Alloxan,  C4H2O4N2,4H2O,  is  an  important  decomposition- 
product  of  uric  acid,  from  which  it  is  obtained  by  oxidation 
with  nitric  acid  :  it  can  also  be  prepared  by  other  methods.  It  is 

362 


§271]  ALLOXAN  AND  ALLANTOINE.  363 

'  mesoxalylurea,  since,  on  treatment  with  alkalis,  it  takes  up  two 
molecules  of  water,  with  production  of  urea  and  mesoxalic  acid: 

CO NH+OHH      CO- OH    NH2 

II  II 

CO        CO  =  CO         -f  CO. 

II  II 

CO NH+OHH      CO-OH     NH2 

Alloxan  Mesoxalic  acid 

Carbon  dioxide  and  parabanic  acid  are  produced  by  the  oxidation 
of  alloxan  with  nitric  acid. 

Alloxan  is  converted  by  reduction  into  alloxantine  : 
2C4H204N2+2H  -  C8H608N4. 

Alloxantine 

Alloxantine  is  also  formed  directly  from  uric  acid  by  evaporating  it 
to  dryness  with  dilute  nitric  acid.  When  treated  with  ammonia, 
it  forms  a  purple-red  dye,  murexide,  C8H8O6N5.  The  formation  of 
murexide  is  employed  as  a  test  for  uric  acid.  Alloxantine  dissolves 
with  difficulty  in  cold  water,  and  gives  a  blue  colour  with  baryta- 
water.  There  is  still  doubt  as  to  the  constitution  of  these  com- 
pounds. 

Allantoine,  C4H6O3N2,  is  formed  in  the  oxidation  of  uric  acid 
with  potassium  permanganate,  a  fact  which  has  an  important  bear- 
ing on  the  constitution  of  this  acid.  Allantoine  has  the  structure 

/NH-CH— NH-CO.NH2 
CO         | 
\NH.CO 

Allantoine 

since  it  can  be  obtained  synthetically  by  heating  glyoxylic  acid 
with  urea: 

H 
/NHlH     HOI— C— [OH+HlHN.CO-NHa 

(X>  IT!  |  Urea  _ 

\NH|H     H0|— CO 

Urea  Glyoxylic  acid 

XNH  •  CH— NH  •  CO  -  NH2 
-»CO 

\NH-CO 

Allantoine 


364  ORGANIC  CHEMISTRY.  [§271 

The  formation  of  alloxan  and  allanto'ine  from  uric  acid  gives  an 
insight  into  its  constitution,  the  production  of  the  first  indicating 

C-N 

the  presence  of  the  complex  C      yC;  and  of  the  second,  the  pres- 
et.N 

sN-C 

ence  of  two  urea-residues,  together  with   the  complex  C<^ 

XN-C* 
These  are  accounted  for  in  the  structural  formula 

NH-CO 

I          I 
CO     C-NH, 

I      II      >co. 
NH— C-NH' 

Uric  acid 

This  formula  also  gives  full  expression  to  the  other  chemical  proper- 
ties of  uric  acid. 

The  following  synthesis  affords  confirmation  of  the  accuracy  of 
the  constitution  indicated.  Malonic  acid  and  urea  combine  to 
form  malonylurea  or  barbituric  acid  : 

NH— CO 

CO     CH2. 
I         I 
NH— CO 

On  treatment  with  nitrous  acid,  this  substance  yields  an  ssonitroso- 
compound  which  can  also  be  obtained  from  alloxan  and  hydro  xyl- 
amine,  violuric  acid : 

NH— CO 
CO     6=NOH. 
NH— CO 

On  reduction,  violuric  acid  gives  aminobarbituric  acid: 

NH— CO 

CO     A<«fcf 

I         I 
NH— CO 


I          I-IHI      | 
0  HHN 


272]  URIC  ACID.  365 

which,  like  the  amines,  adds  on  one  molecule  of  isocyanic  acid  on 
contact  with  potassium  cyanate,  forming 

NH— CO 

I          I/NH\ 
CO     C\        XCO. 

u 

NH— CIO 

This  substance  is  pseudown'c  add,  and  differs  from  uric  acid  only 
in  containing  the  elements  of  another  molecule  of  water.  Boiling 
with  a  large  excess  of  20  per  cent,  hydrochloric  acid  eliminates  this 
molecule  of  water  as  indicated  in  the  formula,  the  treatment  yielding 
a  substance  with  the  constitution  assigned  to  uric  acid,  and  identical 
with  this  compound. 

Uric  acid  dissolves  with  difficulty  in  water,  but  is  soluble  in 
concentrated  sulphuric  acid,  from  which  it  is  precipitated  by  addi- 
tion of  water.  It  forms  two  series  of  salts,  by  exchange  of  one  or 
two  hydrogen  atoms  respectively  for  metals.  Normal  sodium  uratet 
C5H203N4Na2  +  H2O,  is  much  more  soluble  in  water  than  sodium 
hydrogen  urate,  2C5H3O3N4Na  +H2O.  Normal  lithium  urate  is  mod- 
erately soluble  in  water. 

Uric  acid  is  present  in  urine,  and  is  the  principal  constituent  of 
the  excrement  of  birds,  reptiles,  and  serpents:  it  can  be  conveniently 
prepared  from  serpent-excrement.  In  certain  pathological  diseases 
of  the  human  organism,  such  as  gout,  uric  acid  is  deposited  hi  the 
joints  in  the  form  of  sparingly  soluble  primary  salts.  On  account  of 
the  solubility  of  lithium  urate,  lithia-water  is  prescribed  as  a  remedy. 

272.  A  number  of  compounds  with  the  same  carbon -nucleus  as 
uric  acid  occur  in  nature,  partly  in  the  animal,  and  partly  in  the 
vegetable,  kingdom.  To  the  former  belong  hypoxanthine,  C5H4ON4; 
xanthine,  C5H402N4;  and  guanine,  C5H5ON5:  to  the  latter  belong 
the  vegetable  b&sestheobromine,  C7H8O2N4;  and  caffeine,  CgHioO2N4. 
To  assign  a  rational  nomenclature  to  these  substances  and  other 
members  of  the  same  group,  EMIL  FISCHER  regards  them  as  deriva- 
tives of  purine  (273),  the  C-atoms  and  N-atoms  of  which  are 
numbered  as  indicated  in  the  formula 

1N=flCH  NH 

I         I  N/6\/7\ 

HC2    5C-7NH  or        I1     5       8 

\pTT  |2       4 

SN — C.N/^1  \s/ 

4     9  N 


366 


ORGANIC  CHEMISTRY. 


[§272 


Xanthine,  theobromine,  and  caffeine  have  the  following  structural 
formulae  and  rational  names: 


NH— CO 
0 


C— NH, 

I         II          >H; 
NH— C W 

Xanthine  or  2;  6-dioxypurine 


NH- 

io 


N(CH3) 

Dimethylxanthine,  theobromine,  or 
3 :  7-dimethyl-2 ;  6-dioxypurine 


N(CH3)— CO 


(CH3) 


J. 


N(CH3> 


CH. 


Trimethylxanthine,  caffeine,  theine, 
or  1:3:  7-trimethyl-2:  6-dioxypurine 

Theobromine  and  caffeine  result  from  the  introduction  of  methyl- 
groups  into  xanthine. 

Xanthine,  C5H402N4,  is  present  in  all  the  tissues  of  the  human 
body.  It  is  a  colourless  powder,  soluble  with  difficulty  in  water,  and 
possessing  a  weak  basic  character.  On  oxidation,  it  yields  alloxan 
and  urea. 

Theobromine,  C7H802N4,  exists  in  cocoa,  and  is  prepared  from  this 
product.  It  is  only  slightly  soluble  in  water,  and  is  converted  by 
oxidation  into  monomethylalloxan  and  monomethylurea. 

Caffeine  or  theme,  C8H1002N4,  is  a  constituent  of  coffee  and  tea 
It  crystallizes  with  one  molecule  of  water  in  long,  silky  needles,  and 
is  moderately  soluble  in  water.  It  is  generally  prepared  from  tea- 
dust.  On  careful  oxidation  it  yields  dimethylalloxan  and  mono- 
methylurea. 

The  position  of  the  methyl-groups  in  theobromine  and  caffeine  is 
proved  by  the  formation  of  these  oxidation-products. 

There  is  an  evident  resemblance  between  the  constitution  of 
uric  acid  and  that  of  xanthine: 


NH— CO 
CO     C— NH 


NH— C— NH 

Uric  acid 


Xanthine 


These  formulae  indicate  the  possibility  of  obtaining  xanthine  by 
the  reduction  of  uric  acid,  and  up  to  the  year  1897  numerous  un- 


§2731  URIC  ACID.  367 

successful  attempts  were  made  to  prepare  it  by  this  method,  a 
reaction  ultimately  effected  by  EMIL  FISCHER  in  that  year.  He 
has  discovered  several  methods  of  converting  uric  acid  into 
xanthine  and  its  methyl-derivatives  mentioned,  including  one  by 
which  the  manufacture  of  the  therapeutically  important  bases, 
theobromine  and  caffeine,  seems  to  be  possible. 

273.  Direct  replacement  of  oxygen  in  uric  acid  by  hydrogen  does 
not  seem  possible.  EMIL  FISCHER  has,  however,  substituted  chlorine 
for  oxygen  by  means  of  phosphorus  oxychloride.  Various  methods 
of  replacing  the  chlorine  atoms  in  these  halogen  derivatives  by 
other  groups  or  atoms  have  been  devised. 

When  uric  acid  is  treated  with  phosphorus  oxychJoride,  the  first 
product  is  8-oxy-2:6-dichloropurine:  on  further  careful  treatment 
with  the  same  reagent,  this  substance  is  converted  into  2:6:8- 
trich lor  opurine : 


HO-C     C— NHX  -»C1-C     C— NHV 

II    II       >c-ci. 

N— C 1SK  N— C N^ 

Tautomeric  form  of  2:  6: 8-Trichloropurine 

uric  acid 

The  behaviour  of  uric  acid  in  this  reaction  accords  with  the  tauto- 
meric  (235)  formula  of  trihydroxypurine,  the  phosphorus  oxychlo- 
ride  replacing  the  hydroxyl-g-roups  with  chlorine  atoms  in  a  normal 
manner. 

At  0°,  and  in  presence  of  hydriodic  acid  and  phosphonium  iodide, 
trichloropurine  changes  into  di-iodopunne: 

C5HN4C13+4HI  =  C5H2N4I2+3HC1+2L 

Reduction  of  the  aqueous  solution  of  di-iodopurine  with  zinc-dust 
yields  punne,  a  white  crystalline  substance,  melting  at  216°-217°, 
and  very  readily  soluble  in  water.  It  is  a  weak  base,  since  it  does 
not  turn  red  litmus  blue. 

Xanthine  is  thus  obtained  from  trichloropurine. 

Cl-atom  8  in  this  compound  is  very  stable  towards  alkalis, 
whereas  Cl-atoms  2  and  6  are  displaced  with  comparative  ease: 
when  trichloropurine  is  treated  with  sodium  ethoxide,  Cl-atoms 


368- 


ORGANIC  CHEMISTRY. 


[§273 


2  and  6  are  exchanged  for  ethoxyl-groups.  On  heating  the  com- 
pound thus  obtained  with  a  solution  of  hydriodic  acid,  the  ethyl- 
groups  are  replaced  by  hydrogen,  Cl-atom  8  being  simultaneously 
exchanged  for  a  H-atom,  with  formation  of  xan thine: 


N=C-OC2H5 

i     ! 


N=C-OH 


NH-CO 


C2H5O.C     C— NH       ->HO-C     C— NH        ->CO      C     NH 


2:6-Diethoxy-8-chloropurine          Xanthine  (tautomeric  form) 


NH— C— N 

Xanthine 


When  2:6-diethoxy-8-chloropurine  is  heated  with  hydrochloric 
acid,  only  the  ethyl-groups  are  replaced  by  hydrogen,  with  produc- 
tion of  a  compound  of  the  formula 

HN— CO 


CO  C— NH 

II       \r  r] 

I       /C'C1 

HN— C— N 

the  tautomeric  enolic  form  changing  to  the  ketonic  modification. 
On  methylating  this  substance,  its  three  H-atoms  are  exchanged 
for  methyl-groups,  yielding  chlorocaffeme,  which  can  be  converted 
by  nascent  hydrogen  into  caffeine.  This  process,  therefore,  affords 
a  means  of  preparing  caffeine  from  uric  acid. 

EMIL  FISCHER  has  discovered  a  very  characteristic  and  simple 
mode  of  effecting  this  methylation — agitating  an  alkaline,  aqueous 
solution  of  uric  acid  with  methyl  iodide,  whereby  the  four  hydro- 
gen atoms  are  replaced  by  methyl-groups,  with  formation  of  a  tetra- 
methyluric  acid.  On  treating  this  with  phosphorus  oxychloride 
POC13,  chlorocaffeme  is  formed : 

3C503N4(CH3)4+POCl3  =  3C502N4(CH3)3C1+PO(OCH3)3. 
It  can  be  converted  by  nascent  hydrogen  into  caffeine. 

Electro-reduction  of  Purine  Derivatives. 

TAFEL  has  stated  that  caffeine,  xanthine,  uric  acid,  and  sim- 
ilar compounds  reducible  with  difficulty  by  the  ordinary  methods 
readily  take  up  hydrogen  evolved  by  electrolysis.  For  this  pur- 


§273]     ELECTRO-REDUCTION  OF   PUR1NE  DERIVATIVES.      369 

pose  the  compounds  are  dissolved  in  sulphuric  acid,  the  strength 
of  which  is  varied  to  suit  the  particular  compound,  and  lies  between 
50  and  75  per  cent.  This  solution  is  contained  in  a  porous  cell,  and 
has  a  lead  cathode  immersed  in  it.  This  cell  is  placed  in  sulphuric 
acid  of  20  to  60  per  cent,  strength,  which  contains  the  anode.  The 
hydrogen  evolved  at  the  cathode  by  the  current  readily  effects  the 
reduction  of  these  compounds. 

Xanthine  and  its  homologues  take  up  four  atoms  of  hydrogen, 
becoming  transformed  into  deoxy-derivatives: 

C8H1002N4+4H  =  C8H12ON4+H20. 

Caffeine  Deoxycaffelne 

The  deoxy-compounds  are  stronger  bases  than  their  parent-sub- 
stances, which  have  very  weakly  basic  properties. 

The  reduction  of  uric  acid  requires  six  hydrogen  atoms,  and 
yields  pur  one: 

C5H403N4+6H  =  C5H802N4+H20. 

Uric  acid  Purone 

The  oxygen  atom  of  carbon  atom  6  is  replaced  by  hydrogen.  Two 
hydrogen  atoms  are  simultaneously  added  at  the  double  bond  of  the 
uric-acid  molecule: 


[— 6CO  NH— CH2 

2CO     5C— 7NHsXg       -»CO     CH— l>nv 
3NH— 4C— 9NH/8CO      NH— CH— NH/CO 

Uric  acid  Purone 

This  structure  is  proved  by  the  fact  that  on  heating  with  baryta- 
water  purone  yields  two  molecules  of  carbon  dioxide:  it  must, 
therefore,  contain  two  unaltered  urea-residues,  which  necessitates 
the  presence  of  carbonyl-groups  2  and  8.  It  can  be  proved  that 
carbonyl-group  6  is  also  the  group  reduced  in  xanthine  and  its 
homologues. 

Purone  is  neither  a  base  nor  an  acid,  and  is  not  attacked  by 
oxidizing  agents.  When  warmed  with  a  10  per  cent,  solution  of 
caustic  soda,  it  is  transformed  into  isopurone,  which  has  acidic 
properties,  and  is  readily  oxidized. 


370 


ORGANIC  CHEMISTRY. 


[§273 


The  application  of  the  electro-reduction  method  was  at  first 
attended  by  many  difficulties,  yields  varying  between  wide  limits 
being  obtained,  even  when  the  process  was  apparently  carried  out 
in  exactly  the  same  way.  TAFEL  has  both  discovered  the  cause  of 
this  anomaly,  and  indicated  a  method  by  which  the  reaction  can  be 
kept  under  control.  His  investigations  are  of  interest,  and  are 
worth  describing  in  some  detail. 

To  be  able  to  watch  the  course  of  the  reduction-process,  TAFEL 
closed  the  porous  cell  with  a  stopper,  through  which  the  cathode  and 
a  delivery-tube  for  the  gas  were  introduced,  care  being  taken  to 
make  the  connections  air-tight.  A  second  apparatus,  exactly  simi- 
lar to  that  used  for  the  reduction,  but  containing  acid  alone,  with- 
out the  purine  derivative,  was  introduced  into  the  same  circuit. 
Periodically,  the  gas  from  both  was  collected  simultaneously  during 
one  minute.  The  difference  between  these  volumes  of  gas  is  a 
direct  measure  of  the  course  of  the  reduction  during  that  minute, 
since  it  indicates  the  quantity  of  hydrogen  used  in  the  reduction. 

When  this  quantity  is  represented  graphically,  the  abscissse 
standing  for  the  time  which  has  elapsed  since  the  beginning  of  the 
experiment,  and  the  ordinates  for  the  quantity  of  hydrogen  used 
in  the  reduction,  the  normal  course  of  the  reduction  is  indicated 
by  Fig.  71,  since  the  quantity  of  hydrogen  absorbed  in  the  unit  of 


0  TIME  IN  MINUTES 

FIG.  71. — NORMAL  REDUCTION- 
CURVE. 


0.04MQ..PT. 


FIG.  72. — ABNORMAL  REDUC- 
TION-CURVE. 


time  must  diminish  in  the  same  proportion  as  the  quantity  of  unre- 
duced purine  derivative. 

TAFEL  has,  however,  observed  that  the  addition  of  traces  of  a 
platinum  or  copper  salt,  as  well  as  of  certain  other  salts,  very 
quickly  reduces  the  quantity  of  hydrogen  absorbed  to  nearly  zero. 


§273]     ELECTRO-REDUCTION   OF   PURINE  DERIVATIVES.       371 

The  graphic  representation  in  this  case  for  the  addition  of  0-04 
milligrammes  of  platinum  for  each  100  square  centimetres  of  cathode 
surface  is  shown  in  Fig.  72.  This  curve  indicates  that  the  slightest 
contamination  of  the  lead  of  the  cathode  by  certain  other  metals 
is  almost  sufficient  to  stop  the  electro-reduction. 

The  following  considerations  afford  an  insight  into  the  cause  of 
this  phenomenon.  Hydrogen  is  only  evolved  by  the  passage  of  an 
electric  current  through  dilute  sulphuric  acid  when  the  contact- 
difference  of  potential  between  the  electrodes  and  the  solution  ex- 
ceeds a  certain  value.  This  is  a  minimum  when  platinum  elec- 
trodes are  used,  and  very  nearly  coincides  with  the  contact-difference 
of  potential  to  be  expected  on  theoretical  grounds  for  a  reversible 
hydrogen — sulphuric-acid — oxygen -element. 

When  the  cathode  is  made  of  other  metals,  the  contact-difference 
of  potential  is  greater  before  the  evolution  of  hydrogen  begins :  for 
this  a  supertension  (German,.  Uberspannung)  is  necessary.  This 
supertension  has  a  very  large  value  for  lead,  but  as  soon  as  the  least 
trace  of  platinum  or  of  certain  other  metals  is  brought  into  con- 
tact with  the  surface  of  the  lead  cathode,  the  supertension  dis- 
appears, and  with  it  the  power  possessed  by  the  evolving  hydrogen 
of  reducing  purine  derivatives. 

The  explanation  is  that  the  contact-difference  of  potential  regu- 
lates the  energy  with  which  the  discharged  ions  can  react,  for  the 
pressure  under  which  a  discharged  ion  leaves  the  solution  depends 
only  upon  the  contact-difference  of  potential  between  the  electrode 
and  the  liquid  in  which  it  is  immersed.  N ERNST  states  that  by 
varying  the  contact-difference  of  potential  it  is  possible  to  obtain 
pressures  from  the  smallest  fraction  of  an  atmosphere  up  to  many 
millions  of  atmospheres.  Hence,  reductions  unattainable  by  other 
methods,  and  without  supertension,  are  possible  at  cathodes  where 
it  exists. 


SECOND    PART. 

CYCLIC   COMPOUNDS. 


INTRODUCTION. 

274.  With  but  few  exceptions,  the  compounds  described  in  the 
first  part  of  this  book  contain  an  open  chain.  Examples  of  these 
exceptions  are  cyclic  compounds  such  as  the  lactones,  the  anhy- 
drides of  dibasic  acids,  and  the  uric-acid  group.  The  closed  chain 
of  such  compounds  is  very  readily  opened,  and  the  close  rela- 
tionship of  their  methods  of  formation  and  properties  with  those 
of  the  open-chain  derivatives,  makes  it  desirable  to  include  them 
in  a  description  of  the  aliphatic  compounds. 

There  exists,  however,  a  large  number  of  substances  containing 
closed  chains  of  great  stability  towards  every  kind  of  chemical 
reagent,  and  with  properties  differing  in  many  important  respects 
from  those  of  the  aliphatic  compounds.  They  are  called  cyclic 
compounds,  and  are  classified  as  follows: 

A.  Carbocyclic    compounds,    with    a    closed    ring    of    carbon 
atoms  only,  subdivided  into 

1.  Alley  die  compounds,  such  as  the  Ci/c£oparaffin  derivatives 
(121),  and 

2.  Aromatic    compounds,    or    benzene    derivatives.     In    this 
class   are  included   the   compounds   having  condensed  rings,    or 
two  closed   chains  with  atoms   common  to  each.     The  typical 
representative   of   this   type   of   condensed   ring  is   naphthalene, 
Ci0H8,  with  two  benzene-nuclei. 

B.  Heterocyclic    compounds,    with    rings    containing    carbon 
atoms  and  one  or  more  atoms  of  another  element.     This  class 
is  exemplified  by  pyridine,  C5H5N,  and  its  derivatives,  with  a 

373 


374  ORGANIC  CHEMISTRY.  [§  274 

ring  of  five  carbon  atoms  and  one  nitrogen  atom;  furan,  C4H4O, 
with  four  carbon  atoms  and  one  oxygen  atom;  pyrrole,  C4H5N, 
with  four  carbon  atoms  and  one  nitrogen  atom;  thiophen, 
C4H4S,  with  four  carbon  atoms  and  one  sulphur  atom;  pyrazole, 
CsH4N2,  with  three  carbon  atoms  and  two  nitrogen  atoms; 
and  numerous  other  combinations. 

Two  dissimilar  rings  can  also  have  atoms  in  common,  as  in 
quinoline,  CgH7N,  which  contains  a  benzene-nucleus  and  a 
pyridine-nucleus. 

Since  numerous  derivatives  of  all  these  compounds  are  known, 
the  scope  of  the  cyclic  division  of  organic  chemistry  is  much 
more  extended  than  that  of  the  aliphatic  division.*  The  descrip- 
tion of  the  cyclic  group  is,  however,  greatly  simplified  by  the 
fact  that  in  it  the  properties  of  alcohols,  aldehydes,  acids,  etc., 
already  described  for  the  aliphatic  compounds,  are  again  met  with. 

*  In  RICHTER'S  "  Lexikon  der  Kohlenstoffverbindungen,"  319  ring-sys- 
tems are  mentioned. 


A.    CARBOCYCLIC    COMPOUNDS. 


1.  ALICYCLIC    COMPOUNDS. 

I.  q/c/oPropane  Derivatives. 

CBk 

275.  cycloPropane.  C3H6  or  |       /CH2,  is  obtained  bv  the  action 

CH/ 

of  sodium  on  trimethylene  bromide,  CH2Br*CH2*CH2Br  (148).  It 
is  a  gas,  which  liquefies  at  a  pressure  of  five  to  six  atmospheres.  It 
is  not  identical  with  propylene,  CH2:CH'CH3,  since  with  bromine 
it  forms  an  addition-product  only  very  slowly  under  the  influence  of 
sunlight,  yielding  trimethylene  bromide;  nor  is  it  oxidized  by  per- 
manganate. These  properties  and  its  synthesis  prove  its  constitution. 

cycloPropylcarboxylic  acid  is  formed  by  saponifying  the  primary 
product  of  the  interaction  of  ethylene  bromide  and  diethyl  disodio- 
malonate,  and  eliminating  carbon  dioxide: 


CH2 
CH2 

Br 
Br 

Na, 

/COCCUS 
\COOC2H5 

2NaBr  + 
CH2v 

(in>CH 

CH2\     /COOC2H5 

i  y\ 

CH/  \COOC2H, 
•COOH. 

CH2x     yCOOH 
CH2/  \COOH 

II.  cycldButane  Derivatives. 

276.  cycloButane  derivatives  are  obtained  when  diethyl  di- 
sodiomalonate  reacts  with  trimethylene  bromide,  the  diethyl  ester 
of  a  cyc\obutyldicarboxylic  acid  being  formed: 


CH2 

Br 

CH2 

1 

x\ 

CH2 

+  Na2 

C(COOC2H5)2 

-  CH2C(COOC2H5)2+2NaBr. 

CH2 

Br 

\X 
CH2 

375 


376  ORGANIC  CHEMISTRY.  [§  277 

When  heated,  the  dibasic  acid  obtained  by  the  saponification  of  this 
ester  loses  one  molecule  of  carbon  dioxide  (164),  yielding  cyclo- 
butylcarboxylic  acid. 

cycloButane  is  obtained  from  this  acid  by  a  method  applicable 
to  the  preparation  of  other  hydrocarbons.  The  acid  amide  (I.) 
is  converted  by  the  method  of  259  into  cyclobutylamine  (II.).  Treat- 
ment of  this  amine  with  excess  of  methyl  iodide  yields  the  iodide 
of  the  quaternary  ammonium  base  III.,  from  which  the  base  is  then 
prepared.  On  dry  distillation,  it  decomposes  (66)  into  trimethyl- 
amine,  water,  and  q/c?obutylene  (IV.) : 


CH2— CH .  CONH2  CH2— CH .  NH2 

CH2— CH2 


i.  I       I  ->  n.  | 

CH2— CH2 


CH2—  CH  .  N  (CH3)  3OH  CH2—  CH 

-»  III.  ||  -  IV.  |         ||     +N(CH3)3  +  H20. 

CH2—  CH2  CH2—  CH 

On  careful  reduction  with  hydrogen  and  nickel,   q/cZobutylene  is 
converted  into  q/cZobutane. 

CH2—  CHOH 
The  main  product  of  the  oxidation  of  cyclobutanol,  \ 

CH2—  CH2 

CH,  H 

is    cyclopropanal,  >CH-C^,  cyclobutanone  being  also  formed. 


This  reaction  is  remarkable  as  an  illustration  of  the  transformation 
of  a  ring  of  four  carbon  atoms  into  one  of  three  carbon  atoms. 
The  converse  change  of  a  q/cfobutyl-ring  to  a  ci/c/opentyl-ring 

CH2—  CH-CH2OH 

is  exemplified  by  digesting  cydobutykarbinol,  , 

CH2—  CH2 

with  concentrated  hydrobromic  acid,  the  corresponding  bromide 
being  formed.  This  bromide  is  transformed  by  nascent  hydrogen 
into  q/c/opentane,  instead  of  methylcyclobutane. 


III.  q/cZoPentane  Derivatives. 

277.  cycloPentane  derivatives  can  be  obtained  by  a  similar  method 
the  action  of  tetramethylene  bromide  on  diethyl  disodiomalonate. 

When  calcium  adipate  is  submitted  to  dry  distillation,  cyclo- 
pentanone  is  formed: 


27X]  ALICYCLIC  COMPOUNDS.  377 

CH2.CH2-CO  .J0\  CH2-CH2X 

|      >Ca  =  CaC03+  |  >CO. 

CH2.CH2j.CO  O/  CH2.CH2/ 

Calcium  adipate  cycfoPentanone 

It  is  also  obtained  by  heating  adipic  anhydride: 

CH2.CH2-C(\  CH2.CH2X 

\0  =  C02+  |  >CO. 

CH2.CH2.OK  CH2-CH2/ 

The  structure  of  this  compound  is  proved  by  its  oxidation  to  glutaric 
acid: 

CH2-CH2X  CH2-CH2-COOH 

I          >o  -»  I 

CH2-CH/  CH2-COOH 

Glutaric  acid 

This  reaction  presents  a  contrast  to  the  oxidation  of  a  straight- 
chain  ketone  to  two  acids.  The  possibility  of  the  compound  being 
an  aldehyde  is  excluded  by  the  impossibility  of  oxidizing  it  to  a 
monobasic  acid  with  the  same  number  of  carbon  atoms. 

q/c/oPentanone  is  a  constituent  of  the  residue  obtained  in  the 
fractionation  of  methyl  alcohol  (42).  It  is  a  liquid  of  peppermint- 
like  odour,  and  boils  at  130°. 

cycloPentane  is  obtained  by  the  reduction  of  this  ketonic  deriv- 
ative, the  carbonyl-group  taking  up  two  H-atoms,  with  formation 
of  a  CHOH-group.  By  treatment  with  hydriodic  acid,  hydroxyl 
is  first  replaced  by  iodine,  and  finally  by  hydrogen: 

CH,-CH8x  CH2-CHX 

>CO  -»      |  >CHOH     -» 

CH2-CH/  CH2-CH/ 

CH2*  CH2 

>cm   -*    |  >CH2. 

CH2-CH/  CH2-CH/ 

q/c/oPentane  is  a  colourless  liquid  boiling  at  50°.  It  is  a  constituent 
of  Caucasian  petroleum. 

278.  Croconic  acid,  CsHoOo,  is  a  remarkable  q/c?0pentyl-deriv- 
ative,  obtained  by  the  oxidation  of  hexahydroxybenzene  (337) 
in  alkaline  solution.  It  has  an  intense  yellow  colour,  and  is  con- 
verted by  weak  reducing  agents  into  a  colourless  substance,  oxidizable 
to  croconic  acid.  On  oxidation,  croconic  acid  is  transformed  into 
leuconic  acid,  C5Oo,4H2O.  This  compound  has  the  constitution. 


378  ORGANIC  CHEMISTRY.  [§  279 

CO.  CO 


CO,4H2O, 
since  it  yields  a  pentoxime  of  the  formula  (C  I  NOH)5. 

IV.  Higher  Alley  clic  Derivatives. 

279.  cycloHexane  and  its  derivatives  form  the  group  of  hydro- 
aromatic  compounds.  On  account  of  their  relationship  to  the  ter- 
penes  and  camphors,  they  are  described  in  a  separate  chapter 
(363-364). 

Several  methods  are  applicable  to  the  preparation  of  substances 
containing  rings  of  seven  carbon  atoms.  The  first  member  of  this 
class  to  be  prepared  was  suberone,  obtained  by  the  dry  distillation 
of  calcium  suberate: 


CH2-CH2.CH2.COO\  CH2-CH2-CH2X 

>Ca  =  CaC03+  |  >CO. 

H,-CH2.CH2.COO/  CH2.CH2.CH/ 

Calcium  suberate  Suberone 


| 
C 


Hydrolysis  of  the  nitrile  obtained  by  addition  of  hydrocyanic 
acid  to  suberone  and  reduction  of  the  resulting  a-hydroxy-acid 
yield  suberanecarboxylic  acid: 

CH2.CH2-CH2X      /OH          CH2-CH2-CH2\ 

>C(  >CH-COOH. 

CH2-CH2.CH2/     \CN          CH2.CH2.CH/ 

This  acid  is  also  obtained  by  the  interaction  of  ethyl  diazoacetate 
and  benzene,  ethyl  pseudophenylacetate  being  formed  as  an  inter- 
mediate product: 

CH 

HC>/\CH 

C6H6  +  N2HC-COOC2H5   =  r>CH.COOC2H5  +  N2. 

HC^/CH 

CH 

The  acid  corresponding  with  this  ester  can  be  transformed  into  the 
isomeric  isophenylacetic  acid: 
CH 


, 

>CH-COOH. 
H/ 

CH 


§2801 


ALI CYCLIC  COMPOUNDS. 


379 


Reduction   converts  this  isomeride  into  suberanecarboxylic  acid, 
proving  the  presence  of  an  unsaturated  ring  of  seven  carbon  atoms. 
A  thi-rd  mode  of  preparing  cyclip  compounds  with  seven  carbon 
atoms  is  exemplified  by  the  conversion  of  c?/cfohexylmethylaniine  (I.) 
and  other  similar  primary  amines  into  stable  nitrites  (II.) : 

/CH2— CH2\ 

CH<  >CH-CH2.NH2  ->  (CH2)5>CH.CH2.NH2.N02H. 

\CH2— CH/ 

I.  II. 

On  boiling  in  acetic-acid  solution,  these  nitrites  are  transformed 
by  elimination  of  nitrogen  into  the  alcohols  of  the  next  higher 
ring-system : 

(CH2)5>CH-CH2-NH2.NO2H  ->  (CH2)6>CHOH. 

The  conversion  into  suberone  by  oxidation  of  the  alcohol  formed 
from  c7/cfohexylmethylamine  affords  a  proof  of  the  course  of  this 
reaction.  The  synthesis  of  cyclic  compounds  containing  eight 
carbon  atoms  is  effected  similarly. 

280.  The  cyclic  hydrocarbons,  CnH2n,  from  cyclopropane  to  cyclo- 
octane  have  been  definitely  isolated.  The  table  contains  a  com- 
parison of  some  of  their  physical  constants  with  the  corresponding 
constants  of  the  normal  hydrocarbons  of  the  saturated  series 
CnH2n+2,  and  the  unsaturated  series, 


CnH2n  +  2 

CnH2n,  Unsaturated. 

CnH2n>  Cyclic. 

Number 

of  Carbon 

Specific 

Atoms. 

Boiling- 
point. 

Specific 
Gravity. 

Boiling- 
point. 

Specific 
Gravity. 

Boiling- 
point. 

Gravity, 

D4°. 

3 

-45° 

0-536        (0°) 

-  48-2° 

ca.-35° 

4 

1° 

0-600      (0°) 

go 

11°-12° 

0-7038 

5 

36-3° 

0-627    (14°) 

35° 

0-648     (0°) 

49° 

0-7635 

6 

68-9° 

0-658    (20°) 

68° 

0-683  (15°) 

81° 

0-7934 

7 

98  •  4° 

0-683    (20°) 

98° 

0-703  (19-5°) 

117° 

0-8252 

8 

125-60 

0-702    (20°) 

124° 

0-722  (17°) 

147° 

0-850 

The  saturated  cyclic  hydrocarbons  have  higher  boiling-points 
and  much  higher  specific  gravities  (about  0»12)  than  their  unsatu- 
rated isomerides.  The  saturated  hydrocarbons  contain  two  hydro- 
gen atoms  more  than  the  corresponding  defines.  The  correspond- 
ing members  of  both  series  have  almost  the  same  boiling-points,  but 
their  specific  gravities  are  about  0-02  lower. 


2.  AROMATIC   COMPOUNDS. 

CONSTITUTION   OF  BENZENE. 

281.  Certain  substances  found  in  the  vegetable  kingdom  are 
characterized  by  the  possession  of  an  agreeable  aroma:  such  are 
oil  of  bitter  almonds,  oil  of  carraway,  oil  of  cumin,  balsam  of  Tolu, 
gum-benzoin,  vanilla,  etc.  These  vegetable-products  consist  prin- 
cipally of  substances  of  somewhat  similar  character,  which  differ 
from  the  aliphatic  compounds  in  containing  much  less  hydrogen  in 
proportion  to  the  other  elements:  thus,  cymene,  Ci0H14,  is  obtained 
from  oil  of  carraway;  toluene,  CyHg,  from  balsam  of  Tolu;  and 
benzole  acid,  CyHeC^,  from  gum-benzoin.  The  saturated  aliphatic 
compounds  with  the  same  number  of  C-atoms  have  the  formulae 
CioH22,  C7Hi6,  and  C7H14O2,  respectively. 

Before  the  nature  of  the  so-called  aromatic  compounds  had  been 
closely  investigated,  and  on  account  of  their  external  similarity,  it 
was  customary  to  regard  them  as  members  of  a  single  group,  just 
as  ordinary  butter  and  "butter  of  antimony,"  SbCl3,  were  classed 
together  because  of  their  similarity  in  consistency.  This  method 
of  classification  is  still  adopted  for  compounds  with  analogous 
properties,  but  of  imperfectly  understood  constitution,  such  as  the 
bitter  principles,  some  vegetable  alkaloids,  and  many  vegetable  dyes. 

A  closer  study  of  the  aromatic  compounds  has  shown  that  the 
old  and  somewhat  arbitrary  classification  according  to  external  re- 
semblance is  well  founded,  since  all  these  substances  may  be  looked 
upon  as  derivatives  of  one  hydrocarbon,  benzene,  C6H6,  just  as  the 
aliphatic  compounds  can  be  regarded  as  derived  from  methaner 
CH^.  Thus,  on  oxidation,  toluene  yields  benzoi'c  acid,  the  calcium 
salt  of  which  is  converted  into  benzene  by  distillation  with  lime. 
The  dibasic  terephthalic  acid,  C8H6O4,  is  formed  by  the  oxidation  of 
cymene,  and  can  be  similarly  transformed  into  benzene. 

The  discovery  of  this  relation  by  KEKULE  brought  into  promi- 
nence the  question  of  the  constitution  of  benzene,  the  basis  of  all 

380 


§282]  CONSTITUTION  OF  BENZENE.  3^1 

the  aromatic  compounds.  Its  formula,  C6H6,  contains  eight  hydro- 
gen atoms  less  than  that  of  the  saturated  paraffin  with  six  C-atoms, 
hexane,  C6H!  4.  Benzene,  like  other  hydrocarbons  poor  in  hydrogen , 
such  as  C6H12  and  C6H10,  might  be  supposed  to  contain  multiple 
carbon  bonds,  but  its  properties  do  not  admit  of  this  assumption. 
Compounds  with  a  multiple  carbon  bond  readily  form  addition- 
products  with  the  halogens,  are  very  sensitive  to  oxidizing  agents, 
and  easily  react  with  VON  BAEYER'S  reagent  (113):  benzene  lacks 
these  properties.  It  yields  halogen  addition-products  very  slowly, 
whereas  compounds  with  a  multiple  carbon  bond  form  them  instan- 
taneously. It  must,  therefore,  be  concluded  that  benzene  does  not 
contain  multiple  carbon  bonds,  and  that  the  carbon  atoms  in  its 
molecule  are  linked  together  in  a  special  manner. 

Other  considerations  lead  to  the  same  conclusion.  VON 
BAEYER  has  discovered  certain  dibasic  acids,  derivable  from 
cyclohexane. 

Cxi2 — CEi2 

H^C  CH^, 

\      / 

Crl2 — CH2 

by  exchange  of  hydrogen  for  carboxyl.  Removal  of  two  or  four 
hydrogen  atoms  from  these  hexamethylene  derivatives  yields  com- 
pounds the  behaviour  of  which  indicates  that  they  contain  a  mul- 
tiple carbon  bond.  The  abstraction  of  six  hydrogen  atoms  would 
be  expected  to  produce  a  compound  of  an  even  more  unsaturated 
character,  but  a  benzene  derivative  lacking  all  the  properties  con- 
ferred by  a  double  bond  is  formed  instead.  The  elimination  of  the 
third  pair  of  hydrogen  atoms  from  the  hexamethylene  derivative, 
unlike  that  of  the  first  and  second  pair,  occasions  a  sudden  and 
complete  change  in  properties. 

282.  To  understand  the  manner  of  linking  of  the  benzene  carbon 
atoms,  it  is  necessary  to  know  the  relative  distribution  of  its  hydro- 
rcm  and  carbon  atoms.  Two  facts  suffice  to  determine  this  dis- 
tribution. First,  there  are  no  isomerides  of  the  monosubstitution- 
products  of  benzene.  Second ,  the  disubstitution-products  exist  in  three 
isomeric  forms.  Hence,  there  is  only  one  monobromobenzene, 
C6H5Br;  but  three  dibromobenzenes  are  known,  and  are  distin- 
guished by  the  prefixes  ortho,  meta,  and  para. 


382  ORGANIC  CHEMISTRY.  [§  282 

It  follows  from  the  first  of  these  facts  that  the  six  hydrogen  atoms 
of  benzene  are  of  equal  value  (359) :  that  is,  replacement  of  any  one  of 
them  yields  the  same  monosubstitution -product.  Three  formulae, 
in  which  the  six  hydrogen  atoms  are  of  equal  value,  are  possible  for 
benzene: 

I.  C4(CH3)2;    II.  C3(CH2)3;    III.  (CH)6. 

It  has  now  to  be  considered  which  of  these  formulae  agrees  with  the 
second  fact  stated  over-leaf. 

A  disubstitution -product  of  a  compound  with  formula  I.  can  be 
either 

P   j  CH2X  p      CHX2 

C4JCH2X  C4 


No  other  isomerides  are  possible,  so  that  this  formula  is  inadmissible 
as  leading  to  two,  instead  of  to  three,  isomerides. 
With  formula  II.  four  isomerides  seem  possible: 

a.        (CHX    b.        (CHX    c.        ( CX2    d.        ( CH2 
(CH2  (CHX  (CH2  (CH2* 

The  hydrogen  atoms  in  benzene  being  equivalent,  the  CH2-groups 
in  the  benzene  molecule  must  be  similarly  linked,  so  that  a  =  b,  and 
c  =  d:  in  other  words,  the  number  of  possible  isomerides  is  reduced 
to  two.  Formula  II.  cannot  be  accepted  either,  since  it  also  fails  to 
explain  the  formation  of  three  isomeric  disubstitution-products. 

There  remains  only  formula  III.,  in  which  each  carbon  atom  is  in 
union  with  one  hydrogen  atom.  The  question  of  the  constitution 
of  benzene  therefore  narrows  itself  to  this:  given  a  compound  C6H6, 
in  which  each  carbon  atom  is  linked  to  one  hydrogen  atom,  the 
problem  is  to  find  a  formula  which  accounts  for  the  equivalence 
of  all  the  hydrogen  atoms,  the  formation  of  three  disubstitution- 
products,  and  the  absence  of  double  or  multiple  bonds.  It  is  evi- 
dent that  an  open  carbon-chain  formula  cannot  fulfil  the  prescribed 
conditions,  since  the  hydrogen  atoms  attached  to  such  a  chain  con- 
taining terminal  and  intermediate  CH-groups  could  not  be  equi- 


CONSTITUTION  OF   BENZENE. 


383 


valent.     The  six  hydrogen  atoms  can  only  be  of  equal  value  with  a 
ring  of  six  C-atoms: 


HC 


CH 


This  arrangement  of  the  CH-groups  also  fulfils  the  second  condition, 
as  is  evident  from  the  scheme: 


ex 


in  which  the  compounds  C6H4X2,  1:2=1:6,  1:3=1:5,  and  1:4  are 

isomcric.  The  formation  of  three  isomerides  is,  therefore,  also 
accounted  for. 

In  this  scheme,  each  carbon  atom  is  in  union  with  one  hydrogen 
atom  and  two  other  carbon  atoms,  so  that  three  bonds  of  each  car- 
bon atom  are  accounted  for:  it  only  remains  to  ascertain  the  mode 
of  linking  of  the  fourth  carbon  bond.  The  hypothesis  suggested 
by  THIELE  is  described  in  the  next  section. 

283.  THIELE  has  made  a  special  study  of  substances  con- 
taining a  conjugated  linking  (127),  and  has  found  that  addition 
of  two  uni  valent  atoms  to  such  compounds  converts  them  into 
others  with  a  double  bond  at  the  centre  : 

-CH=CH—  CH=:CH—  +  2X  —  CHX—  CIt=CH—  CHX—  . 

To  explain  this  phenomenon,  he  assumes  that  the  whole  of  the 
affinity  of  the  double  bond  is  not  employed,  but  that  a  part— 
the  residual  affinity  —  remains  free  at  atoms  1  and  4,  the  remainder 
being  satisfied  between  atoms  2  and  3,  as  indicated  in  the  scheme 


1234 
C—  C—  C—  C. 


384 


ORGANIC  CHEMISTRY. 


[§284 


The  dotted  lines  denote  partial  valencies.     There  is  a  double  bond 
between  C-atoms  2  and  3,  but  it  is  inactive,  since  addition  takes 
place  only  at  1  and  4. 
,   The  benzene-formula  proposed  by  KEKULE  is  given  in  Fig.  73 : 


FIG.  73. — KEKULE'S  BENZENE- 
FORMULA. 


FIG.  74. — THIELE'S  BENZENE- 
FORMULA. 


THIELE'S  modification  of  KEKULE'S  benzene-formula  has  three 
inactive  bonds,  but  lacks  free  partial  valencies  (Fig.  74).  This 
peculiar  type  of  structure  explains  the  difference  between  the 
properties  of  benzene  and  those  of  other  unsaturated  compounds. 
Such  a  mode  of  linking  is  unknown  in  the  aliphatic  series,  so 
that  it  must  be  the  cause  of  the  properties  peculiar  to  aromatic 
compounds,  and  lacked  by  those  of  the  aliphatic  group.  Hence, 
this  structural  formula  not  only  accounts  for  the  isomerism  of  the 
derivatives  of  benzene,  but  also  explains  the  "  aromatic  "  character 
peculiar  to  them. 


Nomenclature  and  Isomerism  of  the  Benzene  Derivatives. 

284.  The  different  isomeric  disubstitution-products  are  distin- 
guished by  the  prefixes  ortho,  meta,  and  para,  or  the  positions  of 
their  substituents  are  denoted  by  numbers : 


1:2=1:6  substitution-products  are  called  or^o-compounds. 
1:3  =  1:5  meto-compounds. 

1 : 4  para-compounds. 

The  number  of  isomeric  substitution-products  is  the  same  for 


§  284]  SUBSTITUTION-PRODUCTS  OF   BENZENE.  385 

two  similar  or  dissimilar  substituents,  but  not  for  three.     When  the 
three  groups  are  similar,  three  isomerides  exist : 

XXX 


X 

Adjacent  or  Vicinal  Symmetrical  Unsymmetrieal 

1:2:3  1:3:5  1:3:4 

When  one  of  the  groups  is  dissimilar  to  the  other  two,  different 
vicinal  derivatives  result  by  substitution  at  2  and  at  3  respectively, 
and,  for  the  unsymmetrical  compound,  substitution  at  3  produces  a 
different  compound  from  that  resulting  on  exchange  at  4.  For 
four  similar  groups  the  same  number  (three)  of  isomerides  is  pos- 
sible as  for  two,  since  the  two  remaining  hydrogen  atoms  can  be  in 
the  or//io-position,  raefa-position,  or  para-position  to  one  another. 
The  number  of  isomerides  possible  in  other  cases  can  be  readily 
determined. 

An  alkyl-radical  or  other  group  linked  to  a  benzene-residue,  as 
in  C6H5.CH3  or  C6H5.CH2-CH2-CH3,  is  called  a  side-chain,  the 
benzene-residue  being  called  the  nucleus.  Substitution  can  take 
place  both  in  the  nucleus  and  in  the  side-chain:  when  in  the  former, 
it  is  usual  to  refer  to  the  position  of  the  substituent  relative  to  those 
already  present,  the  determination  of  which  is  called  the  determina- 
tion of  position,  or  orientation,  of  the  substituents.  The  methods  of 
orientation  are  given  in  354  to  358. 


PROPERTIES  CHARACTERISTIC  OF  THE  AROMATIC  COM- 
POUNDS: SYNTHESES  FROM  ALIPHATIC  COMPOUNDS. 

285.  The  saturated  hydrocarbons  of  the  aliphatic  series  are  not 
attacked  by  concentrated  nitric  acid  or  sulphuric  acid,  and  only  to 
a  small  extent  by  oxidizing  agents:  their  halogen-substituted 
derivatives  react  with  great  ease.  The  aromatic  hydrocarbons 
differ  from  the  aliphatic  hydrocarbons  in  all  these  respects. 

1.  The  aromatic  hydrocarbons  are  readily  attacked  by  concen- 
trated nitric  acid,  with  formation  of  nitro-compounds: 

C6H5*[H+H(31NO2  =  C6H5-NO2+H2O. 

Nitrobenzene 

These   substances  yield   amino-derivatives  on  reduction,  and  are 
consequently  true  nitro-compounds. 

2.  On  treatment  with  concentrated  sulphuric  acid,  the  aromatic 
compounds  yield  sulphonic  acids: 


C6H5.[H+HO|.S03H  =  C6H5-S03H+H20. 

Benzenesulphonic  acid 

The  sulphur  of  the  SO3H-group  is  linked  to  a  carbon  atom  of  the 
benzene-nucleus,  since  thiophenol,  C6H5'SH,  also  yields  benzene- 
sulphonic  acid  on  oxidation: 

C6H5.SH->C6H5.S03H. 

3.  The  aromatic  hydrocarbons  with  side-chains  are  oxidized 
without  difficulty  to  acids,  the  whole  side-chain  being  usually  oxi- 
dized to  the  carbon  atom  in  union  with  the  nucleus,  with  formation 
of  carboxyl. 

4.  Chlorobenzene  and  bromobenzene  have  their  halogen  atoms 
so  firmly  attached  to  the  phenyl-group,  C6H5,  that  they  are  almost, 
incapable  of  taking  part  in  double  decompositions  with  such  com- 
pounds as  metallic  alkoxides,  salts,  and  so  on. 


§  285]  SYNTHESIS  OF  AROMATIC  COMPOUNDS.  387 

Two  syntheses  of  aromatic  from  aliphatic  compounds  are 
cited  here:  other  examples  are  given  in  the  chapter  on  hydro- 
cyclic  derivatives  (363-364) . 

1.  When   the    vapours   of    volatile    aliphatic    compounds    are 
passed  through  a  red-hot  tube,  aromatic  substances  are  among 
the  products.     The  condensation  of  acetylene,  C2H2,  to  benzene 
is  a  typical  example,  although  passage  through  a  red-hot  tube 
transforms   benzene-vapour   into   acetylene,    proving   that    both 
reactions  are  incomplete.     In  addition  to  benzene,  other  aromatic 
compounds  are  also  formed.     A  synthesis  of   benzene   from  car- 
bon monoxide  is  described  in  337. 

2.  On  treatment  with  sulphuric  acid,  acetone  is  converted  into 
mesitylene,  or  l:3:5-trimethylbenzene  (288): 

3C3H60-3H2O   ==  C9H12. 
Other  ketones  condense  similarly  to  aromatic  hydrocarbons. 


BENZENE  AND  THE   AROMATIC   HYDROCARBONS  WITH 
SATURATED  SIDE-CHAINS. 


Gas-manufacture  and  its  By-products :  Tar. 

286.  The  aromatic  hydrocarbons  are  employed  in  large  quanti- 
ties in  the  manufacture  of  coal-tar  colours,  and  are  obtained  from 
coal-tar,  a  by-product  in  the  manufacture  of  gas.  A  short  descrip- 
tion of  this  process  will  not  be  out  of  place,  since  it  also  yields  other 
products  of  importance  in  the  organic  chemical  industry. 

Coal  is  gradually  heated  in  fire-clay  retorts  of  o -shaped  cross 
section,  and  is  finally  raised  to  a  red  heat:  the  gases  and  vapours 
are  removed  as  completely  as  possible  by  -means  of  exhaust- 
pumps.  Coke  remains  in  the  retorts,  and  is  employed  as  fuel 
and  in  many  metallurgical  processes,  although  for  the  latter  pur- 
pose the  coke  has  usually  to  be  prepared  by  special  means. 

The  distillate  contains  three  main  products.  1.  Gases  (illumi- 
nating-gas). 2.  An  aqueous  liquid,  containing  ammonia  and  other 
basic  substances,  such  as  pyridine  bases.  3.  Tar.  These  products 
are  separated  from  one  another  as  completely  as  possible  by  a  series 
of  treatments.  The  crude  gas  is  passed  over  iron-ore  and  lime,  to 
remove  the  cyanogen  derivatives  and  sulphur  compounds.  The 
former  purifying  material  is  employed  subsequently  for  the  prepara- 
tion of  potassium  ferrocyanide  (257),  an  important  source  of  the 
cyanogen  compounds. 

Tar  is  a  thick,  black  liquid  with  a  characteristic  odour.  Its 
colour  is  due  to  suspended  particles  of  carbon.  It  is  a  complicated 
mixture  of  neutral,  acidic,  and  basic  substances.  The  first  are 
principally  hydrocarbons,  chiefly  belonging  to  the  aromatic  series. 
About  5-10  per  cent,  of  the  tar  consists  of  naphthalene,  and  1-1-5 
per  cent,  of  a  mixture  of  benzene  and  toluene.  Phenol  (294)  is  the 

388 


§  287]  COAL-TAR.  3S9 

principal  acidic  constituent  of  tar.  Basic  substances  are  present 
only  in  small  proportion:  the  chief  are  pyridine,  quinoline,  and 
their  homologues. 

In  the  arts,  the  separation  of  the  tar-products  is  effected  partly 
by  chemical  means,  and  partly  by  fractionation.  The  tar  is  first 
distilled,  a  considerable  portion  remaining  in  the  retort  as  a  black, 
either  soft  or  somewhat  brittle  mass,  known  as  pitch.  'The  dis- 
tillate is  submitted  to  fractional  distillation,  four  fractions  being 
obtained. 

1.  Light  oil,  between  80°  and  170°;    D  0-910-0.950. 

2.  Middle  oil,  or  carbolic  oil,  between  170°  and  230°;    D  1-01. 

3.  Heavy  oil,  or  creosote-oil,  between  230°  and  270°;  D  1-04. 

4.  Green  oil  or  anthracene-oil,  above  270°;  D  !•  10. 

The  light  oil  contains  benzene  and  its  homologues,  which  can  be 
separated  by  further  fractionation.  Only  a  limited  number  of  the 
homologues  of  benzene  are  present  in  the  light  oil — principally 
toluene,  or  methylbenzene,  and  xylene,  or  dimethylbenzene. 

Benzene  and  its  Homologues. 

287.  The  homologues  of  benzene  can  be  prepared  by  the 
method  of  FITTIG,  and  by  that  of  FRIEDEL  and  CRAFTS. 

1.  FITTIG'S    synthesis    is    carried    out    by    treating    bromo- 
benzene,  or,  in  general,  a  hydrocarbon  containing  bromine  in  the 
nucleus,  with  an  alkyl  bromide  or  iodide  and  sodium  (29) : 

=  C6H5— C2H5+2NaBr. 

Ethylbenzene 

A  series  of  by-products  is  sometimes  obtained,  among  them  par- 
affins and  diphenyl,  C0H5-C6H5.  The  yield  of  alkylbenzene  is, 
however,  very  good  when  the  higher  normal  primary  alkyl  iodides 
are  employed. 

2.  FRIEDEL  and  CRAFTS'S  synthesis  is  peculiar  to  the  aromatic 
series,  and  depends  upon  a  remarkable  property  of  aluminium 
chloride.     This  substance  is  obtained  by  the  action  of  dry  hydro- 
chloric-acid gas  on  aluminium-foil.     On  bringing  it  into  contact 
with  a  mixture  of  an  aromatic  hydrocarbon  and  an  alkyl  chloride, 
clouds  of  hydrochloric  acid  are  evolved,  and  hydrogen  of  the  nucleus 
is  exchanged  for  the  alkyl-group: 

C6H5.(HTC1]CH3  =  C6H6-CH3+HCL 


390  ORGANIC    CHEMISTRY.  [§  287 

In  the  synthesis  of  FRIEDEL  and  CRAFTS  more  than  one  alkyl- 
group  is  generally  introduced,  the  monosubstitution-produots  and 
the  higher  substitution-products  being  simultaneously  formed  :  the 
mixture  is  separated  by  fractional  distillation. 

This  reaction  constitutes  a  method  both  for  the  building-up  and 
breaking-down  of  a  hydrocarbon.  When  toluene,  C6H5-CH3,  is 
treated  with  aluminium  chloride,  benzene,  C6H6,  and  xylene, 
C6H4(CH3)2,  are  formed.  The  alkyl-groups  of  one  hydrocarbon  are 
exchanged  for  the  hydrogen  of  the  other.  The  reaction  can  also  be 
effected  by  the  action  of  concentrated  sulphuric  acid  upon  aromatic 
hydrocarbons  with  a  number  of  side-chains. 

3.  By  heating  an  alcohol,  an  aromatic  hydrocarbon,  and  zinc 
chloride  at  270°-300°.  The  zinc  chloride  acts  as  a  dehydrating 
agent  : 


The  following  reactions  are  also  available  for  the  preparation 
of  both  benzene  and  its  homologues: 

4.  Like  the  saturated  aliphatic  hydrocarbons,  the  aromatic 
hydrocarbons  are  obtained  by  the  distillation  of  the  calcium  salts 
of  the  aromatic  acids  with  soda-lime. 


C6H5-  |CO2ca*+caO]H=C6H6+CaCO3. 

5.  Benzene  and  its  homologues  can  be  obtained  by  heating  the 
sulphonic  acids  with  sulphuric  acid  or  hydrochloric  acid,  the  decom- 
position being  facilitated  by  the  introduction  of  superheated  steain: 


C6H3(CH3)2[S03H+HO|H  =  C6H4(CH3)2+H2SO4. 

This  method  can  be  employed  in  the  separation  of  the  aromatic 
hydrocarbons  from  the  paraffins.  When  warmed  with  concentrated 
sulphuric  acid,  the  former  are  converted  into  sulphonic  acids,  soluble 
in  water :  the  paraffins  are  unacted  upon  and  are  insoluble  in  water. 
A  mechanical  separation  is  thus  possible. 

This  method  can  also  be  applied  to  the  separation  of  the  aromatic 
hydrocarbons  from  one  another,  since  some  of  them  are  more  readily 
converted  into  sulphonic  acids  than  others. 

*  ca  =    Ca. 


288] 


BENZENE  AND  ITS   HOMOLOGUES. 


391 


288.  Benzene  and  the  aromatic  hydrocarbons  with  saturated 
side-chains  are  colourless,  highly  refractive  substances,  liquid  at 
ordinary  temperatures,  and  possessing  a  characteristic  odour. 
They  are  immiscible  with  water,  but  mix  in  all  proportions  with 
strong  alcohol.  Some  of  their  physical  properties  are  indicated  in 
the  table. 


Name. 

Formula. 

Boiling- 
point. 

Specific 
Gravity. 

C6H6 

80-4° 

0-874  (20°) 

C6H5-CH3 

110° 

0-869  (16°) 

139° 

0-881     (0°) 

C6H3(CH3)3  (1:3:5) 

164° 

0-865  (14°) 

Ethylbenzene   

136° 

0-883    (0°) 

•zsoProp"!  ben  zone  (Cumene)  .  ..  . 
p-Methyhsopropylbenzene  1 
(Cymene)  /  ' 

CeH55-CH(CH3)2 

O6rl4  <^  plTT  //~1TT    \         A 

L/n  (\jLl3j2  *x 

153° 
175° 

0-866  (16°) 
0-856  (20°) 

The  boiling-points  of  the  isomeric  benzene  derivatives  are 
usually  very  close  together,  but  the  melting-points  display  wide 
divergences.  It  is  an  almost  invariable  rule  throughout  the  entire 
aromatic  series  for^  the  para-compound  to  have  a  higher 
melting-point  than  the  meta- compound  and  the  ortho-compouud. 

Benzene  was  discovered  by  FARADAY,  in  1825,  in  a  liquid 
obtained  from  compressed  coal-gas.  It  melts  at  5*4°. 

The  molecular  weights  of  alcohols,  phenols,  and  aliphatic  acids 
determined  by  the  cryoscopic  method,  with  benzene  as  solvent,  are 
sometimes  twice  as  great  as  the  accepted  values,  whereas  normal 
results  are  obtained  for  other  substances  not  containing  a  hydroxyl- 
group. 

The  formation  of  double  and  multiple  molecules  in  solution  de- 
pends in  large  measure  upon  the  nature  of  the  solvent.  In  addition 
to  benzene,  other  hydrocarbons,  acetic  acid,  and  formic  acid  induce 
the  formation  of  complex  molecules.  The  results  obtained  with  such 
solvents  by  the  cryoscopic  method  for  the  determination  of  molecular 
weights  are  unreliable  (82). 

Xylene,  or  dimethylbenzene,  exists  in  three  isomeric  forms: 
m-xylene  is  the  principal  constituent  of  the  xylene  in  tar,  forming 
70-85  per  cent,  of  the  whole. 


392  ORGANIC  CHEMISTRY.  [§  288 

The  isomeric  xylenes  arc  separable  with  difficulty:  their  boiling- 
points  lie  very  close  together,  that  of  o-xylene  being  142°,  while 
ra-xylene  and  p-xylene  boil  at  139°  and  138°  respectively.  This 
makes  their  separation  by  fractional  distillation  impracticable,  but 
it  can  be  effected  by  treating  tham  with  sulphuric  acid  at  ordinary 
temperatures:  m-xylene  and  o-xylene  go  into  solution  as  sulphonic 
acids,  while  p-xylene  remains  undissolved.  The  sulphonic  acid  of 
the  raeta-compound  and  that  of  the  or^o-compound  can  be  separated 
by  fractional  crystallization  of  their  sodium  salts,  the  ortho-salt  crys- 
tallizing first. 

Cymene,  Ci0H14,  is  closely  related  to  the  terpenes  C10H16,  and 
to  the  camphors  CioH16O,  since  it  can  be  obtained  from  them. 
Cymene  is  a  constituent  of  certain  essential  oils,  such  as  oil  of  carra- 
way,  oil  of  thyme,  and  oil  of  eucalyptus. 


MONOSUBSTITUTION-PRODUCTS  OF  THE  AROMATIC 
HYDROCARBONS. 

I.   MONOHALOGEN  COMPOUNDS. 

289.  Simple  contact  of  the  halogens  with  benzene  does  not 
produce  substitution-products.  Fluorine  reacts  with  this  hydro- 
carbon very  energetically,  decomposing  the  molecule  completely, 
with  formation  of  hydrogen  fluoride  and  carbon  tetrafluoride. 
Chlorine  and  bromine  dissolve  in  benzene,  and  convert  it  slowly 
into  the  addition-products  hexachlorobenzene,  CeHeCle,  and 
hexabromobenzene,  C6H6Br6,  both  reactions  being  accelerated  by- 
sunlight.  Iodine  has  no  action,  except  at  very  high  temperature. 
The  substitution  of  hydrogen  in  benzene  by  chlorine  or  bromine 
can  only  be  effected  in  presence  of  a  catalyst,  anhydrous  ferric 
chloride  or  bromide  being  specially  suitable.  The  process  is 
exemplified  by  the  preparation  of  monobromobenzene,  CeH^Br, 
by  the  addition  of  bromine  drop  by  drop  to  cooled,  dry  benzene 
in  presence  of  a  small  proportion  of  iron-powder.  Ferric 
bromide  is  formed  first,  monobromobenzene  being  then  produced 
with  evolution  of  hydrogen  bromide.  Monoiodobenzene,  C6H5I, 
is  prepared  by  heating  benzene  with  iodine  and  iodic  acid  in  a 
sealed  tube,  the  iodic  acid  oxidizing  the  hydrogen  iodide  formed 
to  iodine  and  water,  and  thus  preventing  it  from  reconverting  the 
monoiodobenzene  into  benzene.  Replacement  by  chlorine  or 
bromine  of  the  hydrogen  of  the  nucleus  in  the  homologues  of 
benzene  also  necessitates  the  presence  of  a  catalyst,  such  as  iron. 
Another  method  of  preparing  the  halogen  derivatives  of  benzene  is 
described  in  307. 

The  halogeri  atom  in  the  monohalogen  derivatives  of  benzene 
can  be  induced  to  react  only  with  great  difficulty.  They  can  be 
boiled  with  alkali,  with  potassium  hydrogen  sulphide,  with 
potassium  cyanide,  or  can  be  heated  with  ammonia,  without 
substitution  of  the  halogen  atom.  The  replacement  of  chlorine 
or  bromine  by  the  amino-group  proceeds  tolerably  smoothly, 
however,  in  presence  of  cupric  sulphate,  a  reaction  exemplified. 

393 


394  ORGANIC  CHEMISTRY.  [§  289 

by  the  formation  of  aniline,  C6H5NH2,  by  heating  monochloro- 
benzene  with  a  concentrated  aqueous  solution  of  ammonia  in 
presence  of  a  small  proportion  of  this  salt  in  an  autoclave  at  a 
temperature  of  about  180°.  Replacement  of  halogen  by  the 
methoxyl-group  can  be  effected  by  the  action  at  220°  of  the 
powerful  reagent  sodium  methoxide. 

The  character  conferred  on  a  halogen  atom  by  union  with  the 
benzene-nucleus  is  in  all  respects  analogous  to  that  possessed 
by  halogen  attached  to  a  doubly-linked  carbon  atom  in  an  aliphatic 
unsaturated  halogen  derivative  (128). 

FITTIG'S  synthesis  (287,  1)  is  one  of  the  few  examples  of  the 
ready  displacement  of  a  halogen  atom  in  union  with  the  benzene- 
nucleus.  Magnesium  reacts  with  an  ethereal  solution  of  mono- 
bromobenzene  in  a  way  resembling  its  action  on  a  similar  solution 
of  an  alkyl  halidc  (75).  It  yields  a  solution  of  a  compound  of  the 
formula  C6H5.Mg.Br,  a  substance  available  for  the  synthesis  of 
tertiary  alcohols  with  the  group  C6H5;  as  described  in  102. 

Monochlorobenzene  is  a  colourless  liquid:  it  boils  without 
decomposition  at  132°,  and  has  a  specific  gravity  of  !•  106  at  20°. 
Monobromobenzene,  B.P.  157°,  sp.  gr.  1-491  at  20°.  Monoiodo- 
benzene,  B.P.  188°,  sp.  gr.,  1-861  at  0°. 

lodobenzene,  and  other  iodine  compounds  substituted  in  the 
nucleus,  can  add  two  atoms  of  chlorine,  with  formation  of  sub- 
stances such  as  phenyliodide  chloride  or  iodobenzene  dichloride, 
C6H5»ICL.  When  digested  with  alkalis,  these  derivatives  give 
iodoso-compounds,  such  as  iodosobenzene,  C6H5'IO,  which  are  amor- 
phous, yellowish  solids.  When  heated,  or  oxidized  with  bleaching- 
powder,  these  compounds  yield  iodoxy-compounds  (German,  lodover- 
bindungeri), 

2C6H5-IO=C6H5.I+C6H5.I02. 

lodoxybenzene 

lodoxybenzene  is  crystalline,  and  explodes  when  heated. 

The  constitution  of  these  compounds  is  inferred  from  their  ready 
conversion  into  iodobenzene,  effected  for  iodosobenzene  by  means 
of  potassium  iodide,  and  for  iodoxybenzene  by  hydrogen  dioxide, 
with  evolution  of  oxygen.  These  substances  would  not  be  so  readily 
converted  into  iodobenzene  if  the  oxygen  were  attached  to  the 
benzene-nucleus  1 


§  290]  MONONITRO-DERIVATIVES.  395 

H.   MONONITRO-DERIVATIVES. 

290.  A  point  of  characteristic  difference  between  the  aromatic 
and  aliphatic  compounds  is  that  the  former  are  very  readily  con- 
verted into  nitro-derivatives  by  the  action  of  concentrated  nitric 
acid  (285,  1).  This  process  is  the  only  method  employed  in  prac- 
tice for  the  preparation  of  aromatic  nitro-compounds.  The 
substance  is  treated  with  a  mixture  of  nitric  acid  and  sulphuric  acid, 
or  with  excess  of  fuming  nitric  acid  of  specific  gravity  1-52: 

C6H5.(H+HQ|.NO2=C6H5.XO2  +  H20. 

If  the  sulphuric  acid  or  an  excess  of  nitric  acid  were  not  present, 
the  water  formed  in  the  nitration  would  dilute  the  nitric  acid 
and  retard  the  action.  This  effect  is  explicable  on  the  assump- 
tion that  dilution  causes  ionization  of  the  nitric  acid,  the 
nitration-process  requiring  an  unionized  acid,  the  hydroxyl-group 
of  which  can  react  with  a  hydrogen  atom  of  the  benzene  to 
form  water.  Increase  in  the  number  of  alkyl-groups  attached 
to  the  benzene-nucleus  is  often  accompanied  by  a  corresponding 
increase  in  the  ease  with  which  nitration  is  effected. 

The  mononitro-compounds  are  very  stable,  and  can  be  dis- 
tilled without  decomposition:  their  nitro-groups  are  very  firmly 
attached  to  the  nucleus.  Unlike  the  primary  and  secondary  nitro- 
compounds  of  the  aliphatic  series,  the  aromatic  nitro-derivatives 
do  not  contain  hydrogen  replaceable  by  metals,  since  their  nitro- 
group  is  linked  to  a  tertiary  carbon  atom:  such  an  exchange  is 
therefore  impossible  (69).  On  reduction,  the  nitro-compounds 
yield  amines,  and  the  reaction  can  be  modified  so  as  to  isolate 
various  intermediate  products  (296-304). 

Most  of  the  mononitro-compounds  have  a  pale-yellow  colour 
and  an  agreeable  odour:  they  are  usually  liquids  heavier  than 
water,  in  which  they  are  insoluble.  They  are  volatile  with  steam. 

Nitrobenzene  is  manufactured  in  large  quantities  in  the  aniline- 
dye  industry.  Cast-iron  vessels  fitted  with  a  stirring  apparatus, 
and  kept  cool  by  water,  are  employed.  They  are  charged  with 
benzene,  and  into  this  a  mixture  of  nitric  acid  and  sulphuric 
acid  is  allowed  to  flow.  At  the  end  of  the  reaction,  the  nitro- 
benzene floating  on  the  surface  of  the  sulphuric  acid,  which 
contains  only  small  quantities  of  nitric  acid,  is  washed  with  water 
and  purified  by  distillation  with  steam. 


396 


ORGANIC  CHEMISTRY. 


290 


Nitrobenzene  is  a  yellowish  liquid:  it  has  an  odour  resembling 
that  of  bitter  almonds,  and  for  this  reason  is  employed  in  per- 
fumery. Its  boiling-point  is  208°,  its  melting-point  5-5°,  and 
its  specific  gravity  1*1987  at  25°.  It  is  poisonous,  inhalation 
of  its  vapour  being  specially  dangerous.  Its  preparation  on  the 
large  scale  is  carried  out  in  order  to  obtain  aniline  by  its  reduction 
(297  and  302). 

Nitrotoluenes. — When  toluene  is  nitrated,  the  chief  products  are 
the  or£/io-compound  and  para-compound :  only  a  small  percentage 


51'4' 


para  100  90      80      70      60     50     40      30      20      10     0 


3-4° 


0   10   20 


40   50   00   TO   80   90  100  ortho 


FIG.    75. — FUSION-CURVE  OF  MIXTURES  OF  O-NITROTOLUENE  AND 

7>-NlTROTOLUENE. 

of  the  meta-compound  is  formed.  The  proportion  of  ortho- 
derivative  is  greater  than  that  of  the  para-isomeride,  as  is  exem- 
plified by  the  percentage-yields  obtained  by  nitration  at  0°,  58*8 
of  o-nitrotoluene,  36-8  of  p-nitrotoluene,  and  4-4  of  m-nitrotoluene. 
Usually,  when  there  is  simultaneous  production  of  ortho-com- 
pounds and  para-compounds,  the  para-isomeride  is  formed  in 
greater  proportion.  o-Nitrotoluene  is  liquid  at  ordinary  tem- 
perature, its  melting-point  being  —3-4°;  p-nitrotoluene  is  solid, 
and  melts  at  51  -4°.  These  isomerides  are  separated  by  a  com- 
bination of  repeated  solidification  by  cooling  and  of  fractional 
distillation.  Fig.  75  represents  the  fusion-curve  ("  Inorganic 
Chemistry,"  237)  of  mixtures  of  o-nitrotoluene  and  p-nitrotolueiie. 


§  291]  MONOSULPHONIC  ACIDS.  397 

Since  the  nitration-product  contains  about  40  per  cent  of  the 
para-isomeride,  its  freezing-point  lies  on  the  para-section  of  the 
curve,  so  that  cooling  causes  crystallization  of  p-nitrotoluene. 
This  substance  can  be  separated  from  the  liquid  residue  by  filtra- 
tion, or  on  the  manufacturing  scale  by  centrifuging.  On  fractional 
distillation  of  the  oil,  o-nitrotoluene,  boiling  at  218°,  distils  first, 
and  subsequently  p-nitrotoluene,  boiling  at  234°.  Several 
repetitions  of  the  fractional  distillation,  with  intermediate  solid- 
ification by  cooling,  finally  yield  an  initial  fraction  so  rich  in  the 
or£/io-compound  that  its  composition  lies  on  the  or^/io-section 
of  the  curve.  On  cooling  this  fraction,  o-nitrotoluene  crystallizes. 

III.    MONOSULPHONIC  ACIDS. 

291.  The  formation  of  these  compounds  is  described  in  285: 
they  are  produced  by  the  action  of  concentrated  sulphuric  acid 
upon  aromatic  compounds.  In  separating  them  from  the  excess  of 
sulphuric  acid,  advantage  is  taken  of  the  ready  solubility  of  their 
calcium  and  barium  salts  in  water:  the  process  is  similar  to  the 
separation  of  ethyl  hydrogen  sulphate  from  sulphuric  acid  (54). 
They  can  also  be  separated  from  their  concentrated  solutions  con- 
taining sulphuric  acid  by  the  addition  of  common  salt  until  no  more 
will  dissolve,  when  the  sodium  salt  of  the  sulphonic  acid  pre- 
cipitates in  the  solid  state.  This  salt  is  dissolved  in  water,  the 
equivalent  quantity  of  mineral  acid  added,  and  the  free  sulphonic 
acid  isolated  by  repeated  extraction  with  ether. 

The  sulphonic  acids  are  colourless,  crystalline  substances, 
generally  hygroscopic,  and  freely  soluble  in  water.  They  can  be 
reconverted  into  the  aromatic  hydrocarbons  by  treatment  at  a 
high  temperature  with  hydrochloric  acid,  or  with  superheated 
-steam  (287,  5),  a  reaction  discovered  by  ARMSTRONG. 

Most  of  the  sulphonates  crystallize  well,  and  are  employed  in 
the  purification  of  the  sulphonic  acids.  On  treatment  with 
phosphorus  pentachloride,  the  latter  are  converted  into  chlorides: 

G6H5  •  SO2  •  OH  ->  C6H5  •  S02  •  Cl. 

The  sulphonyl  chlorides  are  very  stable  towards  cold  water,  being 
but  slowly  reconverted  into  sulphonic  acids.  Benzenesulphonyl 
chloride  melts  at  14- 5°.  Like  the  other  sulphonyl  chlorides,  it 
has  a  veiy  disagreeable  odour. 


398  ORGANIC  CHEMISTRY.  [§§  292,  293 

'The  sulphonamides,  are  formed  by  the  action  of  excess  of  con- 
centrated ammonia  on  the  chlorides: 

C6H5.SO2C1     ->     C6H5.SO2.NH2. 

The  sulphonyl  chloride  first  dissolves,  the  sulphonamide  being 
then  precipitated  by  addition  of  acid. 

They  are  well-crystallized  compounds:  the  determination  of 
their  melting-points  is  often  employed  for  the  identification  of  an 
aromatic  hydrocarbon.  On  account  of  the  strongly  negative 
character  of  the  group  C6H5SO2 — ,  the  hydrogen  atoms  of  the 
NH2-group  are  replaceable  by  metals;  hence  the  sulphonamides 
are  soluble  in  alkalis  and  ammonia. 

The  sulpho-group  can  be  replaced  by  the  hydroxyl-group 
and  the  cyano-group  (292  and  311). 

IV.   MONOHYDRIC  PHENOLS. 

292.  The  phenols  are  compounds  derived  from  the  aromatic 
hydrocarbons  by  replacement  of  one  or  more  of  the  hydrogen 
atoms  of  the  nucleus  by  hydroxyl. 

Phenol,  CeHs'OH,  and  some  of  its  homologues,  such  as  cresol 
and  others,  are  found  in  coal-tar.  During  its  fractional  distillation 
they  are  accumulated  in  the  carbolic  oil  and  creosote-oil  (286). 
They  are  isolated  by  agitating  these  fractions  with  caustic  alkali, 
which  dissolves  the  phenols,  leaving  the  hydrocarbons.  They  are 
liberated  from  the  solution  with  sulphuric  acid,  and  are  then 
separated  by  fractional  distillation.  By  far  the  larger  proportion  of 
the  phenol  of  commerce  is  obtained  from  this  source. 

Phenol  and  its  homologues  can  alsobe  obtained  by  other  methods. 

1.  By  fusion  of  the  salt  of  a  sulphonic  acid  with  alkali: 

C6H5-SO3K+2KOH    .-  C6H5-OK+K2SO3  +  H2O. 

2.  By  the  action  of  nitrous  acid  on  aromatic  amines,  a  method 
analogous  to  the  preparation  of  alcohols  of  the  aliphatic  series 
from  amines  (65).     But  whereas  on  treating  an  aliphatic  amine 
with  nitrous  acid  the  alcohol  is  produced  directly,  in  this  reaction 
very  important  intermediate  products,  the  diazonium  compounds 
(305),  can  be  isolated. 

3.  By  the  action  of   oxygen   upon   benzene   In   presence    of 
aluminium  chloride,  phenol  is  formed. 

293.  The  phenols  are  in  some  respects  comparable  with  the 


§  293]  PHENOLS.  399 

tertiary  alcohols,  since  in  both  the  hydroxyl  is  linked  to  a  carbon 
atom  in  direct  union  with  three  others,  although  in  the  phenols  one 
of  these  bonds  is  of  a  special  kind.  Like  the  tertiary  alcohols, 
therefore,  they  cannot  be  oxidized  to  aldehydes,  ketones,  or  acids 
containing  the  same  number  of  C-atoms.  The  phenols  exhibit 
many  of  the  characteristics  of  the  aliphatic  alcohols:  they  form 
ethers  by  the  interaction  of  alkyl  halides  and  their  alkali-metal 
salts;  they  produce  esters,  forming,  for  example,  acetates  with 
acetyl  chloride.  Phosphorus  pentachloride  causes  the  exchange  of 
Cl  for  their  OH,  although  not  so  readily  as  in  the  aliphatic  series. 
But  in  addition  to  these  properties,  the  phenols  possess  special 
characteristics  due  to  their  much  stronger  acidic  character.  When 
describing  the  separation  of  phenols  from  carbolic  oil  (292) .  it  was 
mentioned  that  they  dissolve  in  caustic  alkalis :  phenoxides,  such  as 
C6H5-ONa,  are  formed.  The  alcohols  of  the  aliphatic  series  do  not 
possess  this  property  in  the  same  degree.  If  they  are  insoluble  in 
water,  they  do  not  dissolve  in  caustic  alkalis,  and  are  only  con- 
verted into  metallic  alkoxides  by  the  action  of  the  alkali-metals. 
This  increase  in  acidic  character  can  only  be  occasioned  by  the 
presence  of  the  phenyl-group;  in  other  words,  the  phenyl-group  has 
a  more  negative  character  than  an  alkyl-group.  Otherwise,  the 
phenols  behave  as  weak  acids:  their  aqueous  solutions  are  bad 
conductors  of  electricity,  and  the  phenoxides  are  decomposed  by 
carbonic  acid. 

It  is  thus  evident  that  the  properties  of  the  hydroxyl-group  are 
considerably  modified  by  union  with  the  phenyl-group.  Inversely, 
the  influence  of  the  hydroxyl-group  on  the  benzene-nucleus  is 
equally  marked:  it  makes  the  remaining  hydrogen  atoms  much 
more  readily  substituted.  Benzene  is  only  slowly  attacked  by  bro- 
mine at  ordinary  temperatures,  but  the  addition  of  brc  mine-water  to 
an  aqueous  solution  of  phenol  at  once  precipitates  2:4 :6-tribromo- 
phenol — a  reaction  employed  in  its  quantitative  estimation.  The 
conversion  of  benzene  into  nitrobenzene  necessitates  the  use  of  con- 
centrated nitric  acid,  but  phenol  yields  nitrophenol  on  treatment 
with  the  dilute  acid.  Phenols  are  also  much  more  readily  oxidized 
than  the  aromatic  hydrocarbons.  When  they  are  heated  with 
zinc  ammonium  chloride,  the  hydroxyl-group  is  replaced  by  the 
amino-group. 

On  distillation  with  zinc-dust,  the  phenols  are  reduced  to  the 
corresponding  hydrocarbons.  They  can  be  detected  by  the 


400  ORGANIC  CHEMISTRY.  [§§294,295 

formation  of  a  violet  coloration  when  ferric  chloride  is  added  to 
their  aqueous  solutions,  probably  due  to  the  production  of  a  ferric 
salt  of  the  phenol. 

294.  Phenol,  or  carbolic  acid,  is  a  colourless  substance,  crystal- 
lizing in  long  needles.     It  melts  at  39-6°,  boils  without  decom- 
position  at    181°,    has   a   characteristic   odour.     On   account   of 
its  powerful  antiseptic  properties,  it  was  introduced  into  surgery 
by  LISTER,  but  to  a  great  extent  its  place  has  been  taken  by 
mercuric  chloride.     Phenol  is  soluble  in  water,  1  part  dissolving 
in  15  at  16°:  it  can  also  dissolve  water.     On  account  of  the  small 
molecular  weight  of  water,  and  the  high  molecular  depression 
of  phenol  (75),  a  small  percentage  of  water  renders  phenol  liquid 
at   ordinary  temperatures   (13).     It   follows  from  the  equation 
AM  =  75,  in  which  M  is  the  molecular  weight   of  water   (18), 
that   A,    the   lowering   of   the   freezing-point  occasioned  by  the 
presence  of  1  per  cent,  of  water,  is  about  4-2°. 

The  hydroxytoluenes,  CH^CeH^OH,  are  called  cresols:  they 
are  present  in  coal-tar,  but  are  usually  prepared  from  the  corre- 
sponding amino-compounds  or  sulphonic  acids.  On  oxidation, 
they  are  completely  decomposed,  but  when  the  hydrogen  of  the 
hydroxyl-group  is  replaced  by  alkyl  or  acetyl,  they  can,  like 
toluene  itself,  be  oxidized  to  the  corresponding  acids.  The 
cresols  resemble  phenol  in  their  behaviour  towards  an  aqueous 

solution  of  bromine.  p-Cresol,  CH3<^  yOH,  is  a  decomposi- 
tion-product of  albumin. 

Thymol  is  also  used  as  an  antiseptic.     It  is  hydroxycymene, 

/CH3  1 

C6H3^OH  3. 

\CH(CH3)2  4 

Acid  sulphuric  esters  of  phenol  are  present  in  urine:  they  result 
from  the  fermentation  (putrefaction)  of  proteins,  since  the  propor- 
tion present  depends  upon  the  extent  of  this  process. 

Ethers. 

295.  A  distinction  is  drawn  between  the  aromatic-aliphatic 
ethers,    such    as    anisole,   C6H5»O»CH3,   and  the  true  aromatic 
ethers,  like  phenyl  ether,  CeHs-O-CoHs.     Compounds  of  the  first 


§  296]  MONOAMINO-COMPOUNDS.  401 

•class  are  formed  by  the  interaction  of  alkyl  halides  and  phen- 
oxides  (293)  : 

C6H5-Q.[Na+T.G:.H5    .*  CeHg-O-CaHs  +  Xal. 

The  true  aromatic  ethers  cannot  be  prepared  by  this  method, 
since  the  halogen  atom  attached  to  the  nucleus  is  exchanged  only 
with  difficulty  (289).  Phenyl  ether  is  obtained  by  heating  phenol 
with  a  dehydrating  agent,  such  as  chloride  of  zinc  or  of  aluminium: 

C6H5-[OHTHJO.CGH5   =  =  CeHs-O-CeHs  +  HaO. 

The  mixed  aromatic-aliphatic  ethers  are  stable  compounds,  and 
resemble  the  true  aliphatic  ethers  closely  in  behaviour.  Many  of 
their  reactions  are  similar  to  those  of  the  aromatic  hydrocarbons 
themselves.  When  heated  to  a  high  temperature  with  a  hydrogen 
halide,  they  yield  a  phenol  and  an  alkyl  halide  : 


Anisole 

The  true  aromatic  ethers,  such  as  phenyl  ether,  are  not  decomposed 
by  hydriodic  acid,  even  at  250°. 

Anisole,  C6H5-O-CH3,  is  a  liquid,  and  boils  at  155°.  Phenetole, 
C6H5-O-C2H5,  is  also  a  liquid,  and  boils  at  172°.  Each  has  a 
characteristic  odour. 

V.    MONOAMINO-COMPOUNDS, 

296.  The  ammo-compounds  of  the  aromatic  series,  with  the 
NH^-group  attached  to  the  ring,  are  almost  exclusively  obtained 
by  reduction  of  the  corresponding  nitro-compounds.  This  is 
effected  by  various  means. 

Amines  can  be  obtained  from  phenols  by  heating  them  at 
300°  with  ammonium  zinc  chloride. 

The  aromatic  amines  are  colourless  liquids,  or  solids,  and 
have  a  characteristic  odour.  They  are  only  slightly  soluble  in 
water.  Their  specific  gravities  approximate  to  1,  and  their 
boiling-points  lie  above  180°.  With  water,  the  aliphatic  amines 
form  stronger  bases  than  ammonia,  but  the  aqueous  solutions  of 
the  aromatic  amines  possess  only  weakly  basic  propsrties:  thus, 
they  do  not  turn  red  litmus  blue,  and  scarcely  conduct  an  electric 
current.  The  aromatic  amines  yield  salts,  however,  although 
these  have  an  acid  reaction  in  solution,  on  account  of  partial 
hydrolysis.  The  negative  character  of  the  phenyl-group, 


402  ORGANIC  CHEMISTRY.  [§  296 

already  alluded  to  in  connexion  with  phenol  (293),  considerably 
modifies  the  nature  of  the  amino-group :  the  difference  in  the 
behaviour  of  diphenylamine  and  of  triphenylamine  in  particular 
betrays  this  influence.  With  strong  acids  the  former  can  yield 
salts,  which,  however,  are  completely  hydrolyzed  by  the  addition 
of  a  considerable  quantity  of  water:  the  second  does  not  unite 
with  acids. 

Substitution  of  the  amino-group  for  hydrogen  produces  the  same 
effect  upon  the  benzene-nucleus  as  substitution  of  the  hydroxyl- 
group  for  hydrogen,  making  the  rest  of  the  hydrogen  atoms  of 
the  nucleus  much  more  easily  replaced:  thus,  aniline  is  readily 
converted  by  bromine-water  into  2:4:6-tribromoaniline.  More- 
over, the  amines  are  much  more  readily  oxidized  than  the  hydro- 
carbons. 

By  means  of  an  alkyl  halide,  the  hydrogen  atoms  in  the  amirio- 
group  of  the  primary  aromatic  amines,  like  those  in  the  amino- 
group  of  the  primary  aliphatic  amines,  can  be  replaced  by  an  alkyl- 
group  (63)  : 

C6H5.NH2+CH3I  =  C6H5-NH(CH3).HL 

Secondary  and  tertiary  bases  and  also  quaternary  ammonium 
bases,  such  as  C6H5.N(CH3)3.OH,  are  known.  The  last  are  as 
strongly  basic  as  the  corresponding  true  aliphatic  compounds. 

The  anilides  are  derivatives  of  aniline,  C6H5»NH2,  and  its  homo- 
logues:  they  are  acid  amides,  in  which  one  amino-hydrogen  atom  has 
been  replaced  by  a  phenyl-group.  Acetoanilide,  C6H5-NH'COCH3, 
employed  as  a  febrifuge  under  the  name  "  antifebrine,"  is  a  type  of 
these  compounds.  The  anilides  are  produced  by  boiling  aniline 
with  the  corresponding  acid.  Acetoanilide  is  obtained  by  heating 
aniline  with  glacial  acetic  acid : 


C6H5.NH[H+HO[OC.CH3  =  C6H5.NH.COCH3+H20. 

MENSCHUTKIN  found  that  the  velocity  of  formation  of  acetoanilide 
is  much  less  for  an  excess  of  aniline  than  for  an  excess  of  glacial 
acetic  acid,  although  on  theoretical  grounds  the  velocity  of  forma- 
tion should  be  the  same  in  both  cases;  for  at  each  moment  it  should 
be  proportional  to  the  product  of  the  concentrations  of  the  glacial 
acetic  acid  (c)  and  of  the  aniline  (c'),  being  therefore  expressed  by 

s  =  k>cc', 
in  which  k  is  constant. 


§  297]  ANILINE.  403 

The  difference  between  theory  and  experiment  admits  of  various 

explanations  :  one  is  that  the  reaction  in  the  two  cases  takes  place 

in   different    media.     The    important  influence  of  the   medium   is 

mentioned  in  71. 

Aldehydes  react  with  aromatic  amines  with  elimination  of  water  : 


Formaldehyde  Methylenediphenyldiamine 

Primary  aromatic  amines  show  the  carbylamine-reaction  :  with 
nitrous  acid  they  yield  diazonium  compounds  (305). 

Aniline. 

297.  Aniline  was  first  obtained  by  the  dry  distillation  of  indigo 
(Portugese,  anil;  from  Sanskrit,  nlla,  dark-blue,  and  nild,  the 
indigo-plant)  ;  hence  its  name.  It  is  manufactured  by  the 
action  of  hydrochloric  acid  and  iron-filings  on  nitrobenzene  con- 
tained in  a  cast-iron  cylinder  fitted  with  a  stirring  apparatus: 

C6H5NO2  +  3Fe  +  6HCl  =  C6H5NH2  +  2H2O  +  3FeCl2. 
It  is  remarkable  that  in  this  process  only  about  one-fortieth  of  the 
hydrochloric  acid  required  by  the  equation  is  needed  for  the 
reduction.  This  is  probably  because  iron-filings  and  w.ater  are 
able  to  effect  the  reduction  in  presence  of  ferrous  chloride.  Lime 
is  added  as  soon  as  the  reduction  is  complete,  and  the  aniline  is 
distilled  with  steam. 

Aniline  is  also  obtained  by  the  electro-reduction  of  nitro- 
benzene (302). 

Aniline  is  a  colourless  liquid,  and,  unless  perfectly  pure,  turns 
brown  in  the  air,  the  colour-change  being  probably  due  to  the  pres- 
ence of  traces  of  sulphur  compounds.  It  is  only  slightly  soluble  in 
water:  it  boils  at  183°,  and  has  a  specific  gravity  of  '1»024  at  16°. 
Formaldehyde  yields  with  aniline  a  remarkable  condensation- 
product,  anhydroformaldehydeaniline,  (C6H5N=CH2)3.  This  sub- 
stance melts  at  40°,  and  dissolves  with  difficulty.  It  is  employed 
in  the  identification  of  both  formaldehyde  (108)  and  aniline. 

An  aqueous  solution  of  free  aniline  gives  a  deep-violet  colora- 
tion with  bleaching-powder  solution,  the  primary  product  in  the 
reaction  being  probably  phenylchloroamine,  CeHs'NHCl,  analo- 
gous to  the  formation  of  chloroamine,  NH2C1,  from  ammonia. 
The  phenylchloroamine  condenses  with  the  aniline  to  form 


404  ORGANIC  CHEMISTRY.  [§  298 

coloured  substances.  An  aniline  salt  in  acid  solution  is  coloured 
dark-green  to  black  by  potassium  dicbromate.  These  two  reac- 
tions, and  that  with  wood  (228) ,  serve  as  tests  for  aniline.  The 
bleaching-powder  reaction  is  particularly  delicate.  The  oxidation 
of  aniline  is  discussed  in  338. 

Homologues  of  Aniline. 

Oriho-toluidine  and  p&ra-toluidine,  CHa-CeH^NH^,  are 
formed  by  the  reduction  of  the  corresponding  nitro-compounds. 
The  or£/io-compound  is  a  liquid,  B.P.  199*4°;  the  para-compound 
is  a  solid,  M.P.  45°.  The  different  solubilities  of  their  oxalic-acid 
salts  afford  a  means  of  separating  them. 

The  monoamino-derivatives  of  the  xylenes  are  called  xylidines. 
Six  isomerides  are  possible,  due  to  differences  in  the  relative  posi- 
tions of  the  methyl  groups  and  the  amino-group  in  the  ring.  Some 
of  the  toluidines  and  the  xylidines  are  employed  in  making  coal- 
tar  colours,  and  are,  therefore,  manufactured  in  large  quantities. 

Secondary  Amines. 

298.  Diphenylamine,  CeHs-NH'CeHs,  melts  at  54°,  and  boils 
at  310°.  It  is  a  type  of  the  true  secondary  aromatic  amines. 
They  are  formed  by  heating  the  hydrochlorides  of  the  primary 
amines  with  the  free  amines : 


C6H5|NH2  •  HC1  +  H)HN  •  C6H5   =  NH4C1  +  HN(C6H5)2. 

Diphenylamine  can  also  be  obtained  by  the  action  of  bromobenzene 
on  potassium  anilide,  C6H5»NHK. 

Diphenylamine  has  an  agreeable,  floral  odour. 

Diphenylamine  is  a  very  sensitive  reagent  for  the  detection  of 
nitric  acid,  which  produces  a  deep-blue  colour  with  its  solution  in 
concentrated  sulphuric  acid.  This  reaction  can  only  be  applied  to 
the  detection  of  nitric  acid  in  the  absence  of  other  oxidizing  sub- 
stances, such  as  bromine-water,  permanganate,  etc.,  since  diphenyl- 
amine  also  gives  a  blue  coloration  with  many  of  these  reagents. 

The  method  of  formation  of  the  mixed  aromatic-aliphatic 
amines,  such  as  methylaniline,  C6H5»NH«CH3,  is  indicated  in  296. 
The  action  of  the  alkyl  iodide  upon  aniline  results  in  the  substitu- 
tion of  more  than  one  hydrogen  atom  of  the  amino-group  by  an 


§  299]  SECONDARY  AND   TERTIARY  AMINES.  405 

alkyl-group,  so  that  a  mixture  of  the  unchanged  primary  and  the 
secondary  and  tertiary  amines  is  formed.  The  secondary  amine  is 
obtained  pure  by  first  replacing  one  hydrogen  atom  of  the  amino- 
group  by  an  acid-radical,  such  as  acetyl,  and  subsequently  treating 
the  acetyl-derivative  with  an  alkyl  iodide. 

To  prepare  such  a  compound  as  methylaniline,  for  example, 
aniline  is  first  converted  into  acetoanilide,  CgHs-NH-COCHs,  by 
boiling  with  glacir.l  acetic  acid.  The  hydrogen  atom  linked  to 
nitrogen  in  this  compound  can  be  replaced  by  sodium,  yielding 
CgHs-NNa-COCHs,  which  on  treatment  with  methyl  iodide  yields 
methylacetoanilide,  C6H5»N(CH3)«COCH3.  Saponification  with 
alkalis  converts  this  compound  into  monomethylaniline. 

The  secondary  aromatic  amines,  like  those  of  the  aliphatic 
series,  are  readily  converted  by  nitrous  acid  into  nitrosoamines, 

NO 

such    as     nitrosomethylaniline,     CeH5-X  <^u  •      LIEBERMANN^ 

Uri3 

reaction    for    nitroso-compounds    is    described    in    "  Laboratory 

Manual,"  XXVII,  n. 

Careful  oxidation  of  the  nitrosoamines  transforms  them  into 
nitroamines,  C6H5'N<^  2.  Compounds  of  this  type  'are  also 
produced  by  the  direct  action  of  fuming  nitric  acid  on  secondary 
amines,  such  as  methylaniline  or  ethylaniline,  three  nitro-groups 
simultaneously  entering  the  nucleus.  FRANCHIMONT  has  prepared 
a  large  number  of  nitroamines  belonging  to  the  aliphatic  series. 

Tertiary  Amines. 

299.  Triphenylamine,  (C6H5)3N',  is  a  type  of  the  true  aromatic 
tertiary  amines :  only  a  few  of  them  are  known.  It  is  obtained  by 
the  action  of  sodium  and  bromobenzene  on  (liphenylamine,  and  is 
a  solid,  melting  at  127°.  It  does  not  possess  a  basic  character. 

It  is  true  that  perchloric  acid,  HC104,  can  unite  with  triphenyl- 
amine,  but  this  acid  displays  a  special  aptitude  for  combination 
with  many  substances,  both  nitrogenous  and  non-nitrogenous. 

PIT 

Dimethylaniline,  C6H5-N<£Tr3,  is  the  most  important  member 

of  the  series  of  mixed  aromatic-aliphatic  tertiary  amines.  They  can 
be  obtained  by  the  action  of  alkyl  halides  upon  anilines,  but  aro 
manufactured  by  heating  aniline  hydrochloride  with  the  alcohol,  a 
method  in  which  alkyl  halides  react  in  the  nascent  state.  Methyl 


406  ORGANIC  CHEMISTRY.  [§  299 

alcohol  and  hydrochloric  acid  yield  methyl  chloride,  and  this  com- 
pound then  .reacts  with  the  aniline. 

On  heating  the  hydrochloride  of  an  alkyl-aniline  at  180°,  in  a 
current  of  hydrochloric-acid  gas,  the  alkyl-groups  are  eliminated, 
with  formation  of  aniline  and  alkyl  chlorides.  When  the  hydro- 
chlorides  of  the  alkyl-anilines  are  strongly  heated,  the  alkyl-groups 
linked  to  nitrogen  are  transferred  to  the  benzene-ring.  This  reac- 
tion can  be  explained  by  assuming  that  decomposition  into  alkyl 
chloride  and  aniline  first  takes  place  as  just  described : 

I.  C6H5.NH(C2H6)HC1  =  C6H5.NH2+C2H5C1. 

The  reaction  indicated  in  equation  II.  ensues: 

II.  C6H5.NH2+C2H6C1  = 

• 

The  formation  of  the  hydrochloride  of  p-toluidine,  by  the  inter- 
action of  methyl  alcohol  and  aniline  hydrochloride  at  a  high  tem- 
perature, is  analogous.  By  this  process  it  is  possible  to  obtain  even 
pentamethylaminobenzene,  C6 (CH3)5  •  NH2. 

The  para-hydrogen  atoms  of  dimethylaniline  and  other  dialkyl- 
anilines  are  replaceable  by  various  groups.  Thus,  dimethylaniline 
reacts  readily  with  nitrous  acid,  with  formation  of  nitrosodimethyl- 
aniline, 


effected  by  the  addition  of  potassium  nitrite  to  the  solution  of  the 
tertiary  base  in  hydrochloric  acid.  This  nitroso-compound  crystal- 
lizes in  well-defined  leaves  of  a  fine  green  colour.  It  melts  at  85°, 
and  yields  a  hydrochloride  crystallizing  in  yellow  needles.  On  oxi- 
dation with  potassium,  permanganate,  the  nitroso-group  is  con- 
verted into  a  nitro-group,  with  formation  of  p-mtrodimethylamline,. 

N(CH3)2  1 


On  boiling  with  caustic  soda,  the  amino-group  of  nitrosodi- 
methylaniline  is  removed,  with  formation  of  dimethylamine  and 
nitrosophenol: 

XT  //TEJ  \  r^TT 

.  lN^LAtl.3^2     .    TT     f\  /">    TT         .,\JO.     .    TT\T//TrT     V 

XTQ  +±12U   =      U6±l4<NQ  +  JtllM  ^±13;2. 

Nitrosophenol 


§  300]  REDUCTION  OF  NITRO-COMPOUNDS.  407 

This  reaction  is  employed  in  the  preparation  of  pure  dimethyl- 
amine  (66). 

The  para-hydrogen  atom  of  dimethylaniline  can  react  with 
substances  other  than  nitrous  acid :  thus,  aldehydes  readily  yield  a 
condensation-product : 

=  C6H5.CH[C6H4N(CH3)2]2. 

The  constitution  of  this  compound  is  inferred  from  its  relation  to 
triphenylmethane.  CH(C6H5)3  (373).  With  dimethylaniline,  car- 
bony  1  chloride  yields  a  p-derivative  of  benzophenone,  C6H5-CO  'C6H5, 
called  MICHLER'S  ketone: 

C6H4.N(CH3)2      1X/C6H4.N(CH3)2 

=  CO  4  +2HC1. 

C6H4.N(CH3)2       \C6H4.N(CH3)2 

Quaternary  Bases. 

Quaternary  bases  are  formed  by  the  addition  of  alkyl  halides 
to  the  tertiary  aromatic-aliphatic  amines,  and  treatment  of  the 
salts  thus  formed  with  moist  silver  oxide.  These  substances  are 
strong  bases.  On  heating,  they  yield  an  alcohol  and  a  tertiary 
amine,  differing  in  this  respect  from  the  aliphatic  ammonium 
bases  (66). 


VI.    INTERMEDIATE  PRODUCTS  IN  THE  REDUCTION  OF  AROMATIC 
NITRO-COMPOUNDS. 

300.  On  reduction,  the  nitro-compounds  of  the  aliphatic  series 
yield  amines  directly,  from  which  the  alkyl-groups  can  be  removed 
by  oxidation:  for  example,  ethylamine  is  converted  into  acetic 
acid  and  ammonia.  In  the  aromatic  series,  on  the  other  hand, 
intermediate  products  can  be  obtained  in  the  reduction  of  nitro- 
compounds,  and  sometimes  also  in  the  oxidation  of  amines.  Only 
the  compounds  derived  from  nitrobenzene  and  aniline  will  be 
described  here,  although  numerous  substitution-products  of  the 
same  type  are  known. 

In  acid  solution  the  nitro-compounds  are  directly  reduced  to 


408  ORGANIC  CHEMISTRY.  l§30 

the  corresponding  amino-derivatives,  but  in  alkaline  solution  yield 
substances  containing  two  benzene-residues.  Nitrobenzene  yields 
in  succession  azoxybenzene,  azobenzene,  hydr azobenzene,  and  aniline: 

1.  Nitro-compound,  C6H5.NO2     O2N.C6H5; 

C6H5.N--N.C6H5; 

2.  Azoxy-compound,  \       / 

3.  Azo-compound,  C6H5-N=N -Cells; 

4.  Hydrazo-compound,  C6H5-NH— NH-C6H5; 

5.  Amino-compound,  C6H5-NH2     H2N-C6H5. 

Azoxybenzene  is  obtained  by  boiling  nitrobenzene  with  alcoholic 
potash,  and  is  also  formed  in  the  oxidation  of  aniline  with  potas- 
sium permanganate  in  alcoholic  solution.  If  forms  light-yellow 
crystals  melting  at  36°.  When  warmed  with  concentrated  sulphuric 
acid,  it  is  transformed  into  p-hydroxyazobenzene: 

C6H6.N- N.C6H6  -»  C6H5.N=N.C6H4.OH. 

\         /  Hydroxyazobenzene 

It  is  readily  attacked  by  various  reducing  agents.  Under  the  influ- 
ence of  direct  sunlight,  concentrated  sulphuric  acid  converts  azoxy- 
benzene into  o-hydroxy 'azobenzene. 

p-Azoxyphenetole,    aH5O.C6H4.N— N.C6H4.OC2H5,    is    distin- 

O 

quished  by  its  power  of  forming  liquid  crystals,  a  property  char- 
acteristic of  a  considerable  number  of  other  substances.  When  heated, 
it  melts  at  134°  to'a  turbid  liquid,  which  suddenly  becomes  clear  at  165°. 
The  crystalline  structure  of  the  turbid  liquid  cannot  be  detected  by  the 
microscope,  but  is  indicated  by  the  double  refraction  exhibited  by  the 
liquid,  and  by  the  formation  of  the  figures  characteristic  of  double- 
refracting  crystals  between  crossed  Nicol  prisms  in  converging  light. 
Turbidity  is  not   an  essential  characteristic  of  liquid  crystals, 
as  VORLANDER  has  discovered  perfectly  clear  liquids  which  display 
phenomena  like  those  of  double-refracting  crystals. 
301 .  Azobenzene,  CeHs  •  N :  N  •  C6H5,  is  formed  by  the  reduction  of 
nitrobenzene  with  a  solution  of  stannous  chloride  in  excess  of  caustic 
potash,  and  also  by  distilling  azoxybenzene  with  iron-filings.     It 
is  produced  along  with  azoxybenzene  by  the  oxidation  of  aniline 
with  potassium  permanganate. 

Azobenzene  forms  well-defined,  orange-red  crystals,  melting  at 
68°,  and  boiling  without  decomposition  at  295°.  It  is  a  very  stable 
compound,  and  is  insoluble  i:.  water.  Its  constitution  follows  from 
its  yielding  aniline  on  reduction. 


§  302]       ELECTRO-REDUCTION  OF  NITRO-COMPOUNDS.  409 


Hydrazobenzene,  C6H5.  NH  —  NH.CeHs,  is  formed  by  the  action 
of  zinc-dust  and  alcoholic  potash  upon  azobenzene  or  nitrobenzene. 
It  is  a  colourless,  crystalline  substance,  and  melts  at  126°.  Strong 
reducing  agents  convert  it  into  aniline:  on  the  other  hand,  it  is 
readily  oxidized  to  azobenzene,  the  transformation  being  slowly 
effected  by  atmosphere  oxygen.  It  is  also  oxidized  to  the  azo- 
compound  by  ferric  chloride. 

The  most  characteristic  reaction  of  hydrazobenzene  is  its  con* 
version  into  benzidine,  whereby  the  benzene-nuclei  are,  as  it  were, 
turned  end  for  end.  This  "  benzidine-transformation  "  is  effected  by 
the  action  of  strong  acids: 


H2N.C6H4— C6H4-NH2. 


Hydrazobenzene  Benzidine 

That  a  diaminodiphenyl  is  thus  formed  is  proved  by  the  conversion 
of  benzidine  into  diphenyl,  C6H5'C6H5.  The  amino-groups  occupy 
the  para-positions: 


By  reducing  azobenzene  in  acid  solution,  benzidine  is  formed 
directly.  It  is  characterized  by  the  sparing  solubility  in  cold  water 
of  its  sulphate. 

The  amino-groups  in  benzidine  are  proved  in  various  ways  to 
occupy  the  para-position:  for  example,  a  hydrazobenzene  the 
p-hydrogen  atoms  of  which  have  been  substituted  cannot  be  con- 
verted into  benzidine.  In  certain  instances  compounds  of  this  kind 
can  undergo  a  remarkable  intramolecular  transformation,  known  as 
the  "semidine-transformation,"  forming  derivatives  of  diphenyla- 
mine  by  the  turning  of  only  one  of  the  benzene-nuclei : 

H/  Q  \XH-XH-C6H4NH-COCHs-»H2X<^""\XH-C0H4NH.COCH3. 


p-Acetaminohydrazobenzene  p-Aminophenyl-p-acetaruino- 

phenylamine 

Electro-reduction  of  Nitro-compounds. 

302.  There  is  reason  to  believe  that  in. the  future  electrolytic 
methods  will  be  used  more  and  more  in  chemical  work,  for  the  elec- 
tric current  affords  a  means  of  varying  the  pressure  and  concentra- 
tion of  the  substances  taking  part  in  reactions  in  the  preparation  of 
organic  compounds,  which  is  not  otherwise  attainable.  By  its  aid 
it  is  possible  to  effect  new  syntheses  or  to  improve  those  already 


410  ORGANIC  CHEMISTRY.  [§  303 

known.     An  explanation  of  this  mode  of  altering  the  pressure  and 
concentration  is  necessary  here. 

Alteration  in  the  contact-difference  of  potential  between  the  elec- 
trodes and  the  electrolyte  causes  considerable  variation  in  the  pres- 
sure at  which  the  discharged  ions  leave  the  solution  (273).  In 
reduction-processes  the  same  effect  is  attained  by  using  different  re- 
ducing agents.  When  a  compound  yields  a  series  of  intermediate 
products  on  treatment  with  different  reducing  agents  of  increasing 
strength,  this  can  also  be  effected  by  increasing  the  contact-difference 
of  potential  (273)  at  the  cathode,  where  hydrogen  is  evolved. 

Regarding  variation  in  the  concentration,  it  must  be  remem- 
bered that  the  electrolytic  process  takes  place  only  in  the  immediate 
neighbourhood  of  the  electrodes.  When  the  surface-area  of  the 
electrodes  is  altered,  the  strength  of  the  current  remaining  the  same, 
the  number  of  ions  discharged  at  unit  surface  varies  in  direct  pro- 
portion: it  is  therefore  possible,  by  selecting  suitable  electrodes,  to 
cause  the  concentration  of  the  ions  discharged  at  them  to  vary 
within  wide  limits.  The  ''strength  "  of  the  reducing  agent  depends 
upon  the  contact-difference  of  potential,  but  its  concentration  is 
controlled  by  the  density  of  the  current  (167).  In  reactions  in 
which  the  discharged  ions  must  interact,  as  in  the  synthesis  of 
dibasic  acids  (loc.  cit.),  a  current  of  high  density  is  necessary:  on 
the  other  hand,  in  reductions  which  must  take  place  as  far  as 
possible  at  all  parts  of  the  liquid,  large  cathodes,  which  give  a  cur- 
rent of  small  density,  must  be  used. 

On  reduction,  nitre-compounds  ultimately  yield  amines,  but 
a  number  of  intermediate  reduction-products  can  be  isolated. 
For  this  reason  the  electro-reduction  of  nitro-benzene  and  its 
derivatives  is  of  both  theoretical  and  practical  importance.  It  is 
possible  to  give  a  complete  and  satisfactory  explanation  of  the 
mechanism  of  this  process. 

303.  A  distinction  must  be  drawn  between  primary  or  elec- 
trolytic, and  secondary  or  chemical,  reduction-products.  The 
primary  process  is 

C6H5.N02  ->  C6H5-NO  -»  C6H5-NHOH  -»  C6H5.NH2. 

Nitrobenzene        Nitrosobenzene        Phenylhydroxyl-  Aniline 

amine 

The  presence  cf  nitrcsobenzene  can  be  detected  by  the  addition 
of  hydroxylamine  to  the  liquid,  with  which  it  reacts  with  loss  of 
one  molecule  of  water,  and  formation  of  diazonium  hydroxide, 
C6H5 -N2-OH:  on  adding  a-naphthol,  an  azo-dye  is  produced  (340). 


§  304]        ELECTRO-REDUCTION  OF  NITRO-COM  POUNDS.          411 

The  formation  of  phenylhydroxylamine  can  be  proved  by  adding 
benzaldehyde,  with  which  it  yields  benzylidenephenylhydroxylamine: 

C6H5.N---CH.C6H5 
C6H5  •  NHOH  +  OCH  .C6H5  =  H2O  + 

Benzaldehyde 

On  rapid  reduction  of  nitrobenzene  dissolved  in  moderately  con- 
centrated sulphuric  acid,  with  addition  of  alcohol  to  increase  the 
solubility,  the  primary  process  just  described  takes  place,  about 
90  per  cent,  of  the  theoretical  yield  of  aniline  being  obtained.  In  a 
strongly  acid  solution,  however,  the  phenylhydroxylamine  is  very 
quickly  converted  into  p-aminophenol: 

C6H5-NHOH  -»HO.C6H4.NH2. 

This  substance  is  not  further  reduced.  Since  phenylhydroxylamine 
undergoes  the  same  transformation,  though  much  more  slowly,  in 
presence  of  more  dilute  acid,  it  is  evident  that  the  theoretical  yield 
of  aniline  cannot  be  obtained,  even  when  the  solvent  is  dilute,  and 
the  velocity  of  reduction  great. 

304.  In  alcoholic-alkaline  solution  the  electro-reduction  of 
nitrobenzene  is  accompanied  by  two  secondary  processes. 

1.  Nitrosobenzene  reacts  with  phenylhydroxylamine,  yielding 
azoxybenzene: 


C6H5.NHOH+C6H5-NO  =  \/  +H20. 

In  presence  of  alkali  this  reaction  proceeds  much  more  quickly  than 
the  further  reduction  of  phenylhydroxylamine,  so  that  only  small 
quantities  of  aniline  are  formed,  and  higher  reduction-products 
of  azoxybenzene,  chief  among  them  hydrazobenzene,  obtained  as 
the  main  part  of  the  yield. 

2.  Hydrazobenzene  is  attacked  by  the  unreduced  nitrobenzene 
with  formation  of  azobenzene  and  azoxybenzene: 

3C6H5.NH.NH.C6H5+2C6H5.N02  =  3C6H5.N:N.C6H5  + 

C6H5-N  -  N.C6H5 
+  \/  +3H20. 

O 

Since  hydrazobenzene  in  alkaline  solution  is  quickly  oxidized  by- 
atmospheric  oxygen  to  azobenzene,  the  yield  of  azobenzene  is  very 
good. 

A  much  higher  contact-difference  of  potential  at  the  cathode 
is  required  to  reduce  hydrazobenzene  to  aniline;    since  for  the 


412 


ORGANIC  CHEMISTRY. 


304 


formation  of  nitrosobenzene  and  phenylhydroxylamine  a  difference 
of  about  0-93  volt  is  necessary,  while  with  a  difference  of  1-47  volt 
only  traces  of  aniline  are  formed  from  hydrazobenzene. 

HABER  has  combined  these  primary  and  secondary  reactions 
in  the  following  scheme,  the  vertical  arrows  indicating  primary, 
and  the  oblique  arrows  secondary,  reactions : 


C6H5.N:N.C6H 


C6H5.NO 

i 

C6H5-NHQH 


C6H6-NH-NH.C6H5 


FIG.  76.  —  HABER'S  ELECTRO-REDUCTION  SCHEME. 


BAMBERGER  pointed  out  that  the  reduction  of  nitrobenzene  by 
purely  chemical  methods  yields  the  same  intermediate  products. 
Thus,  nitrosobenzene  is  formed  by  its  interaction  with  zinc-dust  and 
water.  In  accord  with  this  view  is  the  fact  that  the  velocity  of 
reduction  of  nitrobenzene  by  stannous  chloride  in  presence  of  a  great 
excess  of  hydrochloric-acid  solution  indicates  that  the  reaction  is 
bimolecular,  and  must  therefore  be  represented  by  the  equation 

R-NO+SnCl4  +  H20+(n-2)HCl. 


This  reaction  has  a  measurable  velocity.  The  further  reduction  of 
the  nitroso-compound  to  the  ammo-compound  should  be  very  rapid  : 
experimental  evidence  confirming  this  theoretical  view  is  afforded 
by  the  fact  that  when  nitrosodimethylaniline  is  brought  into  con- 
tact with  stannous  chloride,  it  is  at  once  reduced. 


§  305]  DIAZO-COMPOUNDS.  413 

VII.   DIAZO-COMPOUNDS. 

305.  The  diazo-compounds  of  the  aromatic  series,  discovered  by 
GRIESS  in  1860,  are  not  merely  of  theoretical  importance,  but  play 
an  important  part  in  the  manufacture  of  dyes.  In  the  aliphatic 
series  only  amino-compounds  of  a  special  kind  yield  diazo-com- 
pounds (245),  while  their  formation  is  a  general  reaction  of  the 
primary  aromatic  amines.  The  property  of  undergoing  diazotization 
is  characteristic  of  aromatic  amines. 

All  diazo-compounds  contain  the  group  — N2 — .  HANTZSCH  has 
classified  them  in  two  divisions. 

Ar-N-X 

I.  Substances  with  the  structural  formula  ,  in  which 

N 

Ar  represents  phenyl,  C6H5,  and  its  homologues  and  derivatives. 
The}r  are  called  diazonium  salts,  and  are  analogous  to  the  ammonium 
salts. 

II.  Substances  with  the  structural  formula  Ar-N=N»X.    These 
derivatives  are  called  diazo-compounds,  and  resemble  the  azo-com- 
pounds.     They  are  known  in  two  stereoisomeric  modifications. 

Ar-N 

1.  Compounds  with  the  stereochemical   formula        II.      They 

X.N 

are  called  syndiazo-compounds,  are  unstable,  and  can  be  isolated  only 
in  certain  cases. 

Ar-N 

2.  Compounds  with    the    stereochemical    formula  ,  or 

N-X 

zntidiazo^compounds,  which  are  stable. 

Intrinsically,  the  diazonium  compounds  are  of  slight  import- 
ance, but  the  numerous  transformations  which  they  can  undergo, 
with  formation  of  a  great  number  of  derivatives,  render  them 
much  more  important  than  the  diazo-compounds,  and  account  for 
their  great  significance  in  the  chemistry  of  the  aromatic  compounds. 

Diazonium  compounds  are  formed  by  the  action  of  nitrous  acid 
upon  the  salts  of  aromatic  amines: 

C6H5.NH2.HNO3+HNO2  =  2H2O+C6H5.N2.NO3. 

Aniline  nitrate  ^Benzenediazonium  nitrate 


414  ORGANIC    CHEMISTRY.  [§306 

This  is  effected  by  adding  a  solution  of  sodium  nitrite  to  a  solution 
containing  an  equimolecular  proportion  of  the  amine-salt  and  an 
equivalent  quantity  of  a  free  mineral  acid,  the  reaction-mixture 
being  cooled  by  the  addition  of  ice,  as  the  diazonium  compounds 
decompose  very  readily.  A  solution  of  the  benzenediazonium  salt 
is  thus  obtained. 

The  preparation  in  the  solid  state  of  such  a  salt  as  benzenedia- 
zonium nitrate,  CeHs.Na-NOs,  is  effected  by  passing  nitrogen  tri- 
oxide,  generated  from  nitric  acid  and  arsenious  oxide,  into  a  solution 
of  aniline  in  dilute  nitric  acid.  On  addition  of  alcohol  and  ether, 
the  nitrate  separates  in  crystalline  form.  On  ignition  or  percus- 
sion, the  dry  salt  explodes  with  great  energy,  so  that  only  a  few  deci- 
grammes should  be  isolated  in  the  dry  state.  Almost  all  the  dry  dia- 
zonium salts  are  excessively  explosive,  and  must,  therefore,  be 
handled  with  great  care.  In  aqueous  solution  they  are  harmless, 
and  as  they  yield  derivatives  without  being  isolated,  they  are  seldom 
prepared  in  the  solid  state. 


306.  The  constitution  indicated  for  the  diazonium  salts  is 
inferred  from  the  following  considerations. 

The  group  N2X  of  the  diazonium  compounds,  in  which  X 
represents  an  acid-residue,  is  only  linked  to  one  carbon  atom  cf  the 
benzene-nucleus,  for  all  their  transformations  produce  sub- 
stances containing  a  group  likewise  linked  to  only  one  carbon  atom 
of  the  nucleus. 

In  many  respects  the  group  CeH5'N2 —  behaves  similarly  to  an 
alkali-metal,  and  still  more  to  the  ammonium  radical.  With  strong 
mineral  acids  it  forms  colourless  salts  of  neutral  reaction,  like  KC1 
and  NH^Cl,  while  its  salts  with  carbonic  acid  resemble  the  alkali- 
metal  carbonates  in  having  an  alkaline  reaction,  due  to  hydrolytic 
dissociation.  The  conductivity  of  the  diazonium  salts  of  hydro- 
chloric acid  and  other  acids  indicates  that  they  are  as  strongly 
ionized  as  KC1  and  NH4C1.  Similarly,  diazonium  chlorides  yield 
complex  platinum  salts,  such  as  (C6H5N2Cl)2PtCl4,  soluble  with  diffi- 
culty in  water.  Other  analogous  salts,  such  as  (C6H5N2Cl)AuCl3, 
have  also  been  obtained.  Free  benzenediazonium,  hydroxide, 
C6E5-N2-OH,  is  only  known  in  the  form  of  an  aqueous  solution, 
which  has  a  strongly  alkaline  reaction.  It  is  obtained  by  treating 
the  aqueous  solution  of  the  chloride  with  silver  oxide,  or  by  the 


§307]  DIAZO-COM POUNDS.  415 

addition  of  the  equivalent  quantity  of  baryta-water  to  the  sulphate. 
Like  caustic-potash  solution,  it  is  colourless,  but  through  decom- 
position gradually  deposits  a  flocculent,  resin-like  substance. 

The  existence  of  a  quinquivalent  N-atom  in  the  diazonium  salts, 
as  in  the  ammonium  salts,  must  therefore  be  assumed,  the  basic 
properties  of  the  members  of  each  class  being  due  to  its  presence. 
Two  formulas  are  thus  possible: 


C6H5N=N-X    or 

For  reasons  given  in  308,  the  preference  must  be  given  to  the  second. 

Benzenediazonium  hydroxide  is  a  strong  base,  but  reacts  with 
alkalis  in  a  manner  quite  unknown  among  the  strong  mineral  bases. 
When  a  diazonium  salt  is  added  to  a  strong  solution  of  caustic  potash, 
a  potassium  derivative,  C6H5-N2'OK,  separates  out.  The  reaction 
takes  place  not  only  in  concentrated,  but  also  in  dilute,  solutions. 
When  a  dilute  solution  of  benzenediazonium  hydroxide  is  treated 
with  an  equivalent  quantity  of  caustic  soda  in  dilute  solution,  the 
molecular  conductivity  of  the  mixture  is  considerably  less  than  the 
sum  of  the  two  electric  conductivities  of  the  solutions  separately.  It 
follows  that  a  portion  of  the  ions  (CeH^OX  +  H*  and  Na'+OH', 
which  have  been  brought  into  contact,  have  changed  to  the  non- 
ionized  state — union  of  H'  and  OH';  that  is,  a  salt  must  have  been 
formed. 

Thus,  the  diazonium  hydroxide,  which  is  a  strong  base,  appears 
to  behave  like  an  acid  also.     Since  this  is  very  improbable,  HANTZSCH 
assumes  that  an  equilibrium  exists  in  the  aqueous  solution  between 
the  diazonium  hydroxide  and  the  s?/ndiazohydroxide   (308) : 
C6H5N-OH  ^CeH5N 

III          -         II 
N  HON 

Diazonium         sj/nDiazo- 
hydroxide         hydroxide 

He  supposes  that  the  alkali-metal  compounds  are  derived  from 
the  latter  substance- 

Reactions  of  the  Diazonium  Compounds. 

307.  Many  of  the  reactions  of  the  diazonium  compounds  are 
characterized  by  the  elimination  from  the  molecule  of  the  group 
— N2 —  as  free  nitrogen,  and  its  replacement  by  a  substituent  linked 
by  a  single  bond  to  the  benzene-nucleus.  Extended  research  has 


416  ORGANIC  CHEMISTRY.  \  [§  307 

revealed  the  conditions  best  suited  for  obtaining  nearly  quantita- 
tive results  in  most  of  these  reactions. 

1.  Replacement  of  the  N2-group  by  hydroxyl. — This  reaction  is 
effected  by  allowing  the  aqueous  solution  of  the  diazonium  salt  to 
stand,  or  by  warming  it: 

C6H5.N2.C1+HOH  -=  C6H5-OH+N2+HC1. 

2.  Replacement  by  an  alkoxyl-group,  — O-CnH2n+1. — This  re- 
placement is  carried  out  by  boiling  a  diazonium  salt  with  alcohol: 


C6H5.N2.|HSO4+H|Q.C2H5  = 

In  some  instances,  sunlight  exerts  an  accelerating  influence  on 
reactions  of  the  type  described  in  1  and  2. 

3.  Replacement  of  the  diazonium-group  by  hydrogen. — Under 
certain   conditions   the   diazonium   salts   do   not   yield   alkDxyl- 
compounds  with  alcohols,  but  produce  the  corresponding  hydrogen 
compound,  the  alcohol  being  converted  into  aldehyde: 

NO2  -  C6H4  •  N2  •  Cl  +  C2H5OH  =  N02  •  C6H5  +  C2H4O  +  N2  +  HC1. 

p-Nitrobenzenediazonium  Nitro-  Acetal- 

chloride  benzene  dehyde 

Usually  reactions  2  and  3  proceed  simultaneously;  but  if  the 
benzene-nucleus  is  already  attached  to  several  negative  sub- 
stituents,  such  as  halogen  atoms  or  mtro-groups,  replacement  by 
hydrogen  predominates,  even  with  the  higher  alcohols. 

Another  method  of  substituting  hydrogen  for  the  ammo- 
group  is  mentioned  in  310. 

4.  Replacement  of  the  diazonium-group  by  chlorine. — This  reac- 
tion is  effected  by  treating  a  solution  of  diazonium  chloride  either 
with  cuprous  chloride  dissolved  in  concentrated  hydrochloric  acid 
(SANDMEYER),  or  with  finely-divided  copper  (GATTERMANN)  : 

C6H5.N2.C1  =  C6H5.C1+N2. 

Cuprous  chloride  and  finely-divided  copper  have  a  catalytic 
action :  it  is  probable  that  a  copper  compound  is  formed  as  an  inter- 
mediate product,  and  afterwards  decomposed. 

Replacement  by  bromine  is  carried  out  similarly:  thus,  in  the 
preparation  of  bromobenzene,  a  solution  of  potassium  bromide  is 


I  308]       REACTIONS  OF  THE  DIAZONIUM  COMPOUNDS.          417 

added  to  an  aqueous  solution  of  benzenediazonium  sulphate  con- 
taining free  sulphuric  acid;  on  addition  of  copper-dust  to  this  mix- 
ture, nitrogen  is  evolved,  and  bromobenzene  formed. 

Replacement  by  iodine  takes  place  readily  when  a  warm  solution 
of  potassium  iodide  is  added  to  a  diazonium-sulphate  solution:  it  is 
unnecessary  to  employ  copper  or  cuprous  chloride. 

5.  Replacement  of  the  diazonium-group  by  the  CN  -group.  —  This 
replacement,  too,  readily  takes  place  in  presence  of  copper  com- 
pounds.    The  solution  of  the  diazonium  salt  is   added  to  one  of 
potassium  cuprous  cyanide: 

C6H5.N2.C1+KCN  =  C6H5.CN+N2+KC1. 

This  reaction  is  of  great  importance  for  the  synthesis  of  aromatic 
acids,  which  can  be  obtained  by  hydrolyzing  the  resulting  nitriles. 

6.  Replacement  of  the  diazonium-group  by  sulphur.  —  Addition 
of  a  solution  of  potassium  xanthate  (264)  to  one  of  a  diazonium 
salt  usually  precipitates  the  diazonium  xanthate  : 


On  warming  the  precipitate  with  its  mother-liquor,  nitrogen  is 
evolved,  and  sulphur  becomes  directly  attached  to  the  nucleus, 
with  formation  of  phenyl  xanthate,  C6H5»S-CS-OC2H5.  The  con- 
stitution of  the  product  is  proved  by  its  oxidation  to  benzene- 
sulphonic  acid.  This  reaction  was  discovered  by  LEUCKART,  and 
furnishes  a  valuable  method  for  the  introduction  of  sulpho-groups 
into  benzene  derivatives  at  positions  not  accessible  through  direct 
treatment  with  sulphuric  acid. 

These  reactions  illustrate  the  importance  of  the  diazonium  salts 
as  intermediate  products  in  the  preparation  of  numerous  sub- 
stances. Since  they  are  derived  from  the  amines,  which  are  pre- 
pared by  the  reduction  of  nitro-compounds,  it  is  evident  that  the 
nitration  of  aromatic  derivatives  is  a  reaction  of  great  importance, 
for  the  nitro-group  can  be  replaced  at  will  by  almost  all  other 
elements  or  groups  by  means  of  the  amino-compounds  and 
diazonium  compounds. 

308.  The  reactions  of  the  diazonium  compounds  can  be  explained 
by  assuming  that  they  themselves  do  not  enter  into  reaction,  but 
are  first  converted  into  si/ndiazo-compounds.  which  then  decom- 


418  ORGANIC  CHEMISTRY.  [§  308 

pose  with  evolution  of  nitrogen.     The  formation  of  phenol  may  be 
,  _      represented  thus : 

C6H5  OH  C6H5   OH        C6H5OH 


|_ 
I 


henol 

=  HC1  +     N— N 

synD'iazo- 
hydroxide 


Diazonium 
chloride 


and  that  of  chlorobenzene  thus: 

C6H5          Cl  C6H5  Cl  C6H5C1 


Chlorobenzene 

=  HC1+     N— N  N=N. 


synDiazo- 
Ql  JJ  chloride 

The  reactions  between  diazonium  salts  and  alcohol  are  explained 
as  follows : 
C6H5         OCA       /C6H5  OC2H5\       C6H5-OC2H& 


Cl          H  Cl— H  Cl— H 

H        CeH5 — H  [Formation  of  a  hydrocarbon.] 

N=N  +  -*  NEEN 

Cl  C2H5O         C1OC2H5  [Decomposition  into  HCl and  aldehyde,  C2H4O.J 

As  these  transformations  of  diazonium  salts  cannot  be  repre- 
sented by  the  aid  of  the  other  possible  structural  formula, 
C0H5'Ni=N-X,  it  is  evident  that  it  must  be  rejected  (306). 

Most  of  the  syndiazo-com pounds  are  very  unstable.  They 
change  readily  into  tmtadiazo-compounds,  in  which  it  is  assumed 
that  the  phenyl-group  and  acid-residue  are  not  contiguous,  and 
therefore  can  no  longer  unite : 

Xr<  TT 
V^e-TL; 

N=N 
X 

sj/nDiazo-compound ;  an<iDiazo-compound ; 

CeH5  and  X  can  unite  CeH5  and  X  cannot  unite 

In  certain  cases,  such  as  that  of  the  diazocyanides,  HANTZSCH  has 
been  able  to  isolate  these  intermediate  products,  and  thus  afford  a 
proof  of  these  views.  For  example,  when  cyanides  are  added  to 
diazotized  p-chloroaniline,  C1*C6H4'NH2,  p-chlorobenzonitrile, 
Cl'C6H4-CN,  is  not  immediately  formed:  it  is  possible  to  isolate  a 
yellow  intermediate  product,  C1'C6H4'N2'CN,  which  yields  p- 


U6n5 . 

L 


§  309]       REACTIONS  OF  THE  DIAZONIUM  COMPOUNDS.          419 

chlorobenzonitrile  after  addition  of  copper-dust,  the  action  being 
accompanied  by  an  energetic  evolution  of  nitrogen.  This  yellow 
intermediate  p-chlorobenzenesyndiazocyanide  is,  however,  very  un- 
stable, and  speedily  changes  to  an  isomeride  (the  cmh'-compound) 
which  does  not  react  with  copper-dust.  Stereochemical  theory  thus 
affords  a  satisfactory  explanation  of  the  observed  phenomena. 

309.  The  importance  of  the  diazonium  compounds  is  not  con- 
fined to  reactions  in  which  the  nitrogen  atoms  are  eliminated,  since 
important  derivatives  in  which  they  are  retained  are  known. 

1.  Diazoamino-compounds  are  obtained  by  the  action  of  primary 
and  secondary  amines  upon  diazonium  salts: 


Diazoaminobenzene 

They  are  also  produced  when  nitrous  acid  reacts  with  free  aniline, 
instead  of  with  an  aniline  salt.  It  may  be  supposed  that  in  this 
reaction  benzenediazonium  hydroxide,  or  benzenediazohydroxide 
is  first  formed,  and  is  at  once  attacked  by  a  molecule  of  the  aniline 
still  present: 

I.  C6H5.NH2+HN02  =  C6H5-N2-OH+H2O. 
II.  C6H5.N2.  jOH+H]NHC6H5  =  C6H5.N:N.NHC6H5+H20. 

Benzenediazohydroxide 

The  diazoamino-compounds  are  crystalline,  and  have  a  yellow 
colour.  They  do  not  unite  with  acids.  In  acid  solution,  they  are 
converted  by  treatment  with  nitrous  acid  into  diazonium  salts  : 

C6H5.N:N.NHC6H5+HNO2+2HC1  =  2C6H5.N2.C1+2H20. 

The  most  characteristic  property  of  the  diazoamino-compounds 
is  the  readiness  with  which  they  can  be  transformed  into  isomerides, 
the  aminoazo-compounds: 


C6H5 .  N  -.  N— Nltf  Q     l  -*  C6H6  -  N ;  N<      j>NH2. 

Diazoaminobenzene  Aminoazobenzene 

This  is  effected  by  adding  aniline  hydrochloride  to  a  solution  of 
diazoaminobenzene  in  aniline,  and  warming  the  mixture  on  the 
water-bath. 

The  amino-group  in  aminoazobenzene  is  in  the  para-position  to 
the  azo-group.  When  the  para-position  is  already  occupied,  the 
amino-group  takes  up  the  or^/io-position.  Aminoazobenzene  and 
many  of  its  derivatives  are  dyes  (340) . 


420  ORGANIC  CHEMISTRY.  [§310 

The  equation  indicates  that  the  transformation  of  diazoamino- 
benzene  into  aminoazobenzene  is  a  unimolecular  reaction  ("Inor- 
ganic Chemistry,7'  50).  GOLDSCHMIDT  proved  by  experiment  that 
this  view  is  correct.  He  dissolved  diazoaminobenzene  in  aniline,  and 
determined  the  quantity  of  diazoaminobenzene  still  present  after  the 
lapse  of  known  periods  of  time. 

The  aniline  hydrochloride  added  in  this  reaction  has  merely  a 
catalytic,  accelerating  effect  upon  the  reaction)  as  is  proved,  inter 
aliaj  by  the  uniform  rise  in  the  velocity-constant  with  increase  in 
the  amount  of  aniline  hydrochloride. 

2.  Diazonium  salts  unite  with  tertiary  amines  at  the  para- 
position: 


Dimethylaniline  Dimethylaminoazobenzene 

3.  They  react  similarly  with  phenols,  forming  hydroxyazo-coTn- 
pounds.  This  combination  takes  place  in  presence  of  alkalis: 

C6H5  .  N2  •  [Cr+H|C6H4OH  =  C6H5.N:N.C6H4OH+HC1. 

Phenol  Hydroxyazobenzene 

Important  dyes  are  also  derived  from  hydroxyazobenzene  (341). 

VIII.   HYDRAZINES. 

310.  The  typical  derivative  of  hydrazine  is  phenylhydrazine, 
C6H5»NH«NH2,  referred  to  several  times  in  the  aliphatic  series  in 
connection  with  its  action  on  aldehydes,  ketones,  and  sugars  (103, 
203,  and  209).  It  is  formed  by  the  reduction  of  the  diazonium 
salts;  for  example,  from  benzenediazonium  chloride  by  the  action 
of  the  calculated  quantity  of  stannous  chloride  dissolved  in  hydro- 
chloric acid: 

C6H5.N2.C1+4H  =  C6H5.NH—  NH2.HC1. 

It  can  also  be  obtained  by  transforming  the  diazonium  salt  into  a 
diazosulphonate  by  means  of  an  alkali-metal  sulphite,  reducing  the 
diazosulphonate  with  zinc-dust  and  acetic  acid,  and  eliminating  the 
sulpho-group  by  boiling  with  hydrochloric  acid: 

I.  C6H5.N2.Cl+Na2SO3  =  C6H5.N:N.SO3Na-fNaCl. 

Sodium  diazobenzenesulphonate 

II.  C6H5.N:N.SO3Na+2H  =  C6H5  •  NH  .  NH  .  SO3Na. 

Sodium  phenylhydrazinesulphonate 

III.  C6H5.NH.NH.SO3Na+H2O  =  C6H5-NH.NH2+NaHSO4. 

Phenylhydrazine 


§  311]  PHEN  YLH  YDRAZINE.  42  1 

In  practice,  this  apparently  roundabout  way  is  simple,  since  the 
intermediate  products  need  not  be  isolated.  It  is  sufficient  to 
mix  solutions  of  the  diazonium  salt  and  of  the  sulphite,  add  the 
acetic  acid  and  zinc-dust,  and  filter  off  the  excess  of  zinc.  The 
filtrate  is  then  boiled  with  fuming  hydrochloric  acid,  whereupon 
the  hydrochloride,  C6H5'NH-NH2-HC1,  separates  out,  being  soluble 
with  difficulty  in  water,  and  almost  insoluble  in  hydrochloric  acid. 

Phenylhydrazine  is  a  colourless,  oily  liquid,  turning  brown  in 
the  air.  Its  melting-point  is  19  •  6°,  and  its  boiling-point  241°: 
when  boiled  under  ordinary  pressure,  it  undergoes  slight  decom- 
position. It  is  only  slightly  soluble  in  water. 

Phenylhydrazine  is  decomposed  by  energetic  reduction  into 
aniline  and  ammonia.  It  is  very  sensitive  towards  oxidizing  agents, 
its  sulphate  being  oxidized  to  the  diazonium  salt  by  mercuric  oxide. 
Oxidation  usually  goes  further,  however,  the  nitrogen  being  elimi- 
nated from  the  molecule.  Thus,  an  alkaline  copper  solution  con- 
verts it  into  water,  nitrogen,  and  benzene.  Phenylhydrazine  has  a 
wholly  basic  character:  it  yields  well-defined  crystalline  salts. 

Phenylhydrazine  is  proved  thus  to  have  the  constitutional  for- 
mula C6H5  •  NH»NH2.  A  secondary  amine  is  converted  by  nitrous 
acid  into  the  corresponding  nitrosoamine: 


Monomethylaniline          Nitrosomethylaniline 

On  careful  reduction,  this  substance  yields  methylphenylhydrazinef 
C6H5'N<£,jj2,  which  can  also  be  obtained  from  phenylbydrazine 

by  the  action  of  sodium,  one  hydrogen  atom  being  replaced  by  the 
metal.  On  treatment  of  this  sodium  compound  with  methyl  iodide, 
the  same  methylphenylhydrazine  is  formed: 


C6H5  •  NH--  NH2  -T»  C6H5  •  N  <        2  ->  C6H5  -  N  < 


IX.  AROMATIC  MONOBASIC  ACIDS:     BEKZOlC   ACID    AND    ITS 
HOMOLOGUES. 

311.  Benzole  acid,  CeHs-COOH,   can  be  prepared  by  many 
methods,  of  which  the  most  important  will  be  described. 


422  ORGANIC  CHEMISTRY.  [§  311 

1.  By  the  oxidation  of  any  aromatic  hydrocarbon  with  a  side- 
chain: 


Beinq;  inexpensive,  toluene  is  specially  serviceable  for  this  purpose. 
In  the  manufacture  of  benzoi'c  acid,  toluene  is  not  directly  oxidized  ? 
but  is  treated  at  its  boiling-point  with  chlorine.  Benzotrichloride, 
C6H5-CC13,  is  first  formed,  and  is  converted  into  benzole  acid  by 
heating  with  water: 

OH 
C6H5.CC1+HOH-H2O  =  C6H5.COOH+3HC1. 


Benzole  acid  thus  prepared  often  contains  traces  of  chlorobenzow 
acid,  C6H4C1.COOH. 

2.  By  the  oxidation  of  aromatic  alcohols  or  aldehydes,  such  as 

benzyl  alcohol,  C6H5.CH2OH,  or  benzaldehyde,  C6H5C^:  also  by 

the  oxidation  of  alcohols,  aldehydes,  or  ketones  with  longer  side- 
chains:  in  fact,  from  all  compounds  containing  a  side-chain  with 
cms  carbon  atom  directly  linked  to  the  benzene-nucleus. 

3.  By  the  introduction  of  the  nitrile-group  into  the  benzene- 
nucleus,  and  hydrolysis  of  the  benzonitrile,  C6H5-CN,  thus  formed. 
The  introduction  of  the  nitrile-group  can  be  effected  in  two  ways. 

(a)  By  diazotizing  aniline,  and  treating  the  diazonium  salt  with 
potassium  cyanide  (307,  5). 

(b)  By  distilling  potassium  benzenesulphonate  with  potassium 
cyanide: 

C6H5-S03K+KCN  =  C6H5.CN+K2S03. 

4.  By  the  action  of  carbon  dioxide  and  sodium  on  bromoben- 
zene,  whereby  sodium  benzoate  is  formed: 

C6H5Br+C02+2Na  =  NaBr+C6H5.CO2Na. 

5.  By  the  action  of  various  derivatives  of  carbonic  acid,  other 
than  carbon  dioxide,  upon  benzene,  substances  readily  convertible 
into  benzoi'c  acid  are  formed. 

(a)  In  presence  of  aluminium  chloride,  benzene  and  carbonyl 


§  312]  BENZOIC  ACID.  '  423 

chloride   react   together,   with   formation   of   benzoyl  chloride,   the 
chloride  of  benzole  acid,  and  hydrochloric  acid: 

C6H5|H+C1|.COC1  =  C6H5.COC1+HC1. 

Benzoyl  chloride 

Benzoyl  chloride  is  converted  into  benzoic  acid  by  treatment  with 
hot  water. 

(b)  Benzene  and  aluminium  chloride  react  with  carbamyl  chlo- 
ride, Cl  -CONE^  (formed  by  passing  carbonyl  chloride  over  heated 
ammonium  chloride),  yielding  benzamide,  the  amide  of  benzoic  acid  : 

C6H5|H  +  C1|-CONH2   --  C6H5-CONH2  +  HC1. 

Benzamide 

(c)  Bromobenzene  is  converted  by  sodium  and  ethyl  chloro- 
formate  into  ethyl  benzoate: 


C6H5fBr  +  Cl  |.COOC2H5 


312.  Benzoic  acid  is  a  constituent  of  many  natural  resins  and 
balsams,  such  as  gum-benzoin,  Peru-balsam,  and  Tolu-balsam.  A 
derivative,  hippuric  acid  (242),  is  present  in  the  urine  of  horses.  It 
was  formerly  prepared  principally  from  gum-benzoin,  from  which 
source  the  benzoic  acid  used  as  a  medicament  is  still  sometimes 
obtained.  It  is  a  white  solid,  crystallizing  in  leaf-like  crystals 
melting  at  121-4°.  It  sublimes  readily,  and  boils  at  250°:  it 
volatilizes  with  steam,  and  can  be  purified  by  steam-distillation. 
Its  alkali-metal  salts  dissolve  readily  in  water,  most  salts  of  other 
bases  being  soluble  with  difficulty. 

The  solubility-curve  ("Inorganic  Chemistry,"  235)  of  benzoic 
acid  has  been  the  subject  of  careful  investigation,  on  account  of  its 
interesting  character  (Fig.  77).  The  solubility  increases  somewhat 
rapidly  with  increase  of  temperature  up  to  90°  (AB).  At  this  tem- 
perature, the  acid  melts  beneath  the  water,  so  that  two  liquids  result: 
one  is  an  aqueous  solution,  containing  11»2  per  cent,  of  acid  (point 
B)\  the  other  consists  principally  of  the  acid,  containing  95-88  per 
cent,  (point  D).  Above  this  temperature  an  effect  like  that  described 
in  74  is  produced:  the  mutual  solubility  of  these  layers  is  repre- 


424 


ORGANIC  CHEMISTRY. 


[§313 


sented  in  the  part  BCD  of  the  curve,  of  which  BC  corresponds  with  the 
aqueous,  and  DC  with  the  acid  layer.    The  composition  of  the  two 


.  100 


O  >-  TEMPERATURE  90°  U6°  121.4° 

FIG.  77. — SOLUBILITY-CURVE  OF  BENZOIC  ACID  IN  WATER. 

layers  becomes  more  and  more  alike  as  the  temperature  rises,  since 
the  water  dissolves  more  benzoic  acid,  and  the  acid  more  water.  At 
116°  they  are  identical  in  composition:  that  is,  the  liquid  has  again 
become  homogeneous. 

If  more  benzole  acid  is  added  to  the  acid  layer  only,  at  90°,  it 
is  necessary  to  raise  tha  temperature  to  keep  all  the  acid  fused:  the 
line  DF  is  thus  obtained,  ending  at  F  at  the  melting-point  of  pure 
benzoic  acid,  121*4°.  DF  therefore  represents  the  melting-point- 
curve  of  the  acid,  on  addition  of  increasing  amounts  of  water. 


Derivatives  of  Benzoic  Acid. 

313.  Benzoyl  chloride,  C6H5-COC1,  can  be  obtained  by  the  action 
of  phosphorus  pentachloride  or  oxy chloride  upon  benzoic  acid,  or 
by  the  method  of  311,  5a.  It  is  a  liquid  of  disagreeable  odour,  and 
boils  at  194°.  It  is  manufactured  by  treating  benzaldehyde, 

TT 

CfcHs'CQ,  with  chlorine.     Unlike  acetyl  chloride,  which  is  rapidly 

decomposed,  it  is  very  slowly  acted  upon  by  water  at  ordinary 
temperatures. 

Benzoyl  chloride  is  employed  in  the  introduction  of  the  benzoyl- 
group,  C6H5-CO — ,  into  compounds.  This  is  effected  by  a  method 


§  313]  DERIVATIVES  OF  BENZOIC  ACID.  425 

discovered  by  BAUMANN  and  SCHOTTEX,  which  consists  in  agitat- 
ing the  substance  in  alkaline  solution  with  benzoyl  chloride. 

Amines  are  readily  benzoylated  by  suspending  their  hydrochlo- 
rides  in  benzene,  adding  the  equivalent  quantity  of  benzoyl  chloride, 
and  heating  until  evolution  of  hydrogen  chloride  has  ceased. 

Benzole  anhydride,  C6H5CO-O-COC6H5,  is  formed  by  the  inter- 
action of  a  benzoate  and  benzoyl  chloride: 

C6H5  •  CO  -  O  |Na+Cl|  •  OCC6H5  =  NaCl  +C6H5CO  •  O  -  COC6H5. 

At  ordinary  temperatures  it  is  very  stable  towards  water,  but  is 
decomposed  when  boiled  with  it,  yielding  benzoic  acid. 

The  formation  of  ethyl  benzoate  (311,  5c)  is  sometimes  employed 
as  a  test  for  ethyl  alcohol,  since  it  possesses  a  characteristic  pepper- 
mint-like odour. 

Benzamide  (311,  56),  C6H5-CONH2,  can  be  prepared  by  the 
action  of  ammonia  or  ammonium  carbonate  on  benzoyl  chloride. 
It  is  crystalline  and  dimorphous,  melting  at  130°.  It  is  stated  in 
96  that  the  influence  of  the  negative  acetyl-group  causes  the  hydro- 
gen atoms  of  the  amino-group  in  acetamide  to  be  replaceable  by 
metals.  Benzamide  displays  this  property  to  an  even  greater 
extent,  on  account  of  the  more  negative  character  of  the  benzoyl- 
gro'up;  for  the  values  of  the  dissociation-constants  for  acetic  acid 
and  for  benzoic  acid  respectively  are  104/:  =  0-18  and  104/:  =  0-60. 
When  the  silver  compound  of  benzamide  is  treated  with  an  alkyl 
iodide  at  ordinary  temperatures,  an  O-ether,  benzoic  iminoether, 

OC2H5 
C6H5-CC  ,  is  formed.      The  constitution  of  this  substance  is 

NH 

proved  by  its  yielding  ammonia  and  alcohol,  instead  of  ethylamine 
and  benzoic  acid,  when  treated  with  alkalis.  When,  however,  the 
silver  compound  is  treated  with  an  alkyl  iodide  at  100°,  a  JV-alkide, 


C6H5'(X  ,  is  formed.    This  is  proved  by  the  decomposition  of 

0 

the  latter  substance  into  ethylamine  and  benzoic  acid,  so  that  the 
silver  compound  must  have  different  constitutions  at  ordinary  tem- 
peratures and  at  100°  (262). 


426  ORGANIC  CHEMISTRY.  [§  314 

Benzonitrile,  Cells  -CN,  the  methods  of  producing  which  are 
described  in  311  ,  3,  can  also  be  prepared  similarly  to  the  aliphatic 
iiitriles:  for  example,  by  the  action  of  phosphoric  oxide  upon 
benzamide.  It  is  a  liquid  with  an  odour  resembling  that  of  bitter 
almonds,  and*  boils  at  191°.  It  has  all  the  properties  characteristic 
of  the  aliphatic  nitriles. 

The  homologues  of  benzole  acid,  such  as  the  toluic  acids, 
CH3-C6H4.COOH,  the  xylic  acids,  (CHg^CeHa-COOH,  and  so  on, 
are  crystalline  solids,  very  slightly  soluble  in  water.  They  are 
prepared  by  methods  analogous  to  those  employed  for  benzoi'c 
acid. 

X.   AROMATIC  ALDEHYDES  AND  KETONES. 
Aldehydes. 

TT 

314.  Benzaldehyde,  CeHs-C,  is  the  best-known  of  the  aromatic 


aldehydes.  Like  the  aliphatic  aldehydes,  it  is  formed  by  the  oxida- 
tion of  the  corresponding  alcohol,  benzyl  alcohol,  C6H5.CH2OH, 
and  by  distillation  of  a  mixture  of  a  benzoate  and  a  formate.  It 
is  manufactured  by  heating  benzol  chloride,  CeHs-CHCU,  with  water 
and  calcium  carbonate,  a  method  the  aliphatic  analogue  of  which 
is  of  no  practical  importance: 


The  following  methods  are  employed  in  the  preparation  of  the 
homologues  of  benzaldehyde. 

1.  When  ethyl  chloro-oxalate  is  brought  into  contact  with  an 
aromatic  hydrocarbon  in  presence  of  aluminium  chloride,  the  ethyl 
ester  of  an  a-ketonic  acid  is  produced: 

C0H(i  +  ClCO— COOC2H5  =  C6H5-CO-COOC2H5  +  HC1. 

Ethyl  chloro-oxalate 

The  free  acid  is  obtained  by  saponification,  and  on  dry  distillation 
loses  CO2,  with  formation  of  the  aldehyde : 

CftH5.CO-C02H  -  C6H5.CQ  +  C02. 

2.  An  aromatic  hydrocarbon  is  treated  with  a  mixture  of  carbon 
monoxide  and  hydrochloric  acid  in  presence  of  aluminium  chloride 


§  315]  ALDEHYDES.  427 

and  a  trace  of  cuprous  chloride.     It  may  be  assumed  that  formyl 
chloride,  HCOC1,  is  obtained  as  an  intermediate  product  : 

CH3-C6H5+C10CH     =  CH.-C.H4-C0+HC1. 

315.  Benzaldehyde  occurs  in  the  natural  product,  amygdalin, 
C2oH27OiiN  (256);  on  this  account  it  is  called  oil  of  bitter  almonds. 
It  is  a  liquid  of  agreeable  odour,  is  slightly  soluble  in  water,  boils 
at  179°,  and  has  a  specific  gravity  1-0504  at  15°.  It  has  most  of 
the  properties  of  the  aliphatic  aldehydes:  it  is  readily  oxidized,  even 
by  the  oxygen  of  the  atmosphere  (especially  when  exposed  to  sun- 
light), reduces  an  ammoniacal  silver  solution  with  formation  of  a 
mirror,  yields  a  crystalline  addition-product  with  sodium  hydrogen 
sulphite,  adds  on  hydrocyanic  acid  and  hydrogen,  forms  an  oxime 
and  a  phenylhydrazone,  and  so  on. 

It  displays,  however,  points  of  difference  from  the  fatty  alde- 
hydes. Thus,  with  ammonia  at  the  ordinary  temperature  it  does 
not  yield  a  compound  like  acetaldehyde-ammonia,  but  produces 
hydrobenzamide,  (C6H5CH)3N2,  formed  by  the  union  of  three 
molecules  of  benzaldehyde  and  two  molecules  of  ammonia: 

+2H3N  =  (C6H5GH)3N2  +  3H20. 


At    —20°,  however,  ammonia  combines  with  benzaldehyde  to 
benzaldehy  de-ammonia,  2C0H5-CHO,NH3,  probably 

NH[CH(C6H5).OH]2, 

which  separates  in  plates  melting  at  45°.  After  a  time  it 
decomposes  into  hydrobenzamide,  benzaldehyde,  and  water.  It 
is  an  intermediate  product  in  the  preparation  of  hydrobenzamide. 

The  behaviour  of  the  aromatic  aldehydes  towards  alcoholic 
potash  is  characteristic,  one  molecule  of  the  aldehyde  being  oxi- 
dized, and  the  other  reduced  (c/.,  however,  108).  Thus,  benzalde- 
hyde yields  potassium  benzoate  and  benzyl  alcohol: 

C6H5-COOK+C6H5.CH2OH. 


The  aromatic  aldehydes  condense  readily  with  dimethylaniline 
or  phenols,  forming  derivatives  of  triphenylmethane  (373)  : 


428  ORGANIC   CHEMISTRY.  [§  315 


e^ 
-t     <+H2°- 


C«H4OH  CCH4OH 


Benzaldehyde  also  reacts  very  readily  with  aniline.  When  a 
mixture  of  equal  volumes  of  the  two  substances  is  heated  gently, 
drops  of  water  separate,  and,  on  cooling,  benzylideneaniline, 
CeHg-CHrN-CeHfi,  crystallizes. 

The  action  of  chlorine  on  benzaldehyde  is  described  in  313. 

Benzaldehydephenylhydrazone,  Cells  •CH:N«NH -Cells,  is  very 
readily  precipitated,  with  evolution  of  considerable  heat,  by 
addition  of  benzaldehyde  drop  by  drop  to  a  sulphurous-acid 
solution  of  phenylhydrazirie.  It  forms  pale-yellow  crystals, 
melting  at  152°,  and  is  transformed  by.  the  action  of  violet  or 
ultraviolet  light  into  a  scarlet-red  isomeride,  the  original  colour 
being  restored  by  exposure  to  yellow  or  green  light. 

AUTOXIDATION. 

It  has  been  observed  that  during  the  oxidation  of  various  sub- 
stances in  the  air  as  much  oxygen  is  rendered  "active"  as  is  taken 
up  by  the  substance  under  oxidation:  this  phenomenon  is  displayed 
in  the  atmospheric  oxidation  of  benzaldehyde.  If  it  is  left  for 
several  weeks  in  contact  with  water,  indigosulphonic  acid,  and  air, 
the  same  amount  of  oxygen  is  absorbed  in  oxidizing  the  indigo 
derivative  as  in  converting  the  benzaldehyde  into  benzoi'c  acid.  VON 
BAEYER  has  shown  that  benzoyl-hydrogen  peroxide  C6H5COOOH, 
is  formed  as  an  intermediate  product,  and  oxidizes  the  indigosul- 
phonic acid,  being  itself  reduced  to  benzole  acid: 

C6H6-CHO+02  =  C6HS.CO-0-QH; 

C6H5- CO -O -OH  +  Indigo  =  CCH5-COOH  +  Oxidized  indigo. 
The  oxidation  of  benzaldehyde  in  the  air  must  be  considered,  there- 
fore, to  take  place  thus: 

CeH5-CHO+O2  =  C6H5-CO-O-OH; 
C6H5.CO.O-OH+C6H&.CHO  =  2C6H5.(X)OH. 

VON  BAEYER  has,  in  fact,  proved  that  benzoyl-hydrogen  peroxide 
dissolves  when  added  to  benzaldehyde,  but  that  the  liquid  gradually 
solidifies  to  pure  benzole  acid. 


§  316]  KETONES.  429 


Ketones. 

316.  The  aromatic  ketones  can  be  subdivided  into  the  mixed 
aromatic-aliphatic  ketones  and  the  true  aromatic  ketones.  The 
typical  member  of  the  first  class  is  acetophenone,  CeHs'CO'CHa. 
It  can  be  obtained  by  leading  a  mixture  of  the  vapours  of  acetic 
•acid  and  benzoic  acid  over  thorium  oxide,  ThO2,  at  430°-460°; 
or  more  readily  by  the  addition  of  aluminium  chloride  to  a 
mixture  of  benzene  and  acetyl  chloride.  It  is  a  crystalline  sub- 
stance of  agreeable  odour,  melting  at  20°  and  boiling  at  200°: 
it  is  slightly  soluble  in  water,  and  possesses  all  the  properties  of 
the  aliphatic  ketones.  It  is  employed  as  a  soporific  under  the 
name  "  hypnone." 

Benzophenone,  CeHs-CO-CeHs,  is  a  true  aromatic  ketone,  and 
can  be  obtained  by  the  dry  distillation  of  calcium  benzoate,  or 
by  the  action  of  benzene  and  aluminium  chloride  upon  benzoyl 
chloride,  or  carbonyl  chloride.  This  compound,  although  a  true 
aromatic  derivative,  behaves  exactly  like  an  aliphatic  ketone:  on 
reduction,  it  yields  benzhydrol,  CeHs-CHOH-CeHs;  benzpinacone, 

(C6H5)2C  --  C(C6H5)2.     . 

•  •  is  simultaneously  formed  (150). 

OH     OH 

Although  there  is  still  uncertainty  as  to  FRIEDEL  and  CRAFTS'S 
synthesis  of  the  homologues  of  benzene  (287,  2),  BOESEKEN  has 
explained  the  mechanism  of  this  synthesis  of  aromatic  ketones. 
He  has  proved  that  the  acid  chloride  first  unites  with  the  aluminium 
chloride  • 

C6H5COC1  +  A1C13  =  CflH6COCl-AlCl,. 

On  addition  of  one  molecule  of  benzene,  one  molecule  of  hydrochloric 
acid  is  evolved,  with  formation  of  a  crystalline  compound: 

C6H5.COC1-A1C13+C6H6  =  C6H5.CO'C0H5.A1C13  +  HC1. 

When  this  compound  is  treated  with  water,  a  quantitative  yield  of 
the  ketone  is  obtained: 


The  reaction  therefore  takes  place  in  three  stages. 

BOESEKEN'  s  researches  on  the  FRIEDEL  and  CRAFTS  reaction 
have  proved  the  scheme  indicated  to  be  inapplicable  to  other 
examples  of  this  synthetic  method.  In  the  formation  of  ketones, 


430 


ORGANIC  CHEMISTRY. 


:§317 


equimolecular  proportions  of  the  acid  chloride  and  aluminium 
chloride  are  necessary;  but.  in  other  modifications  of  the  method 
only  a  trace  of  aluminium  chloride  is  required  to  start  the  reaction, 
the  chloride  being  merely  a  catalyst.  This  type  of  reaction  is 
exemplified  by  the  formation  of  diphenylmethane,  C6H5*CH2 -Cells, 
from  benzyl  chloride  and  benzene  (372).  Usually,  aluminium 
chloride  acts  only  as  an  " activator"  when  it  enters  into  combi- 
nation with  the  organic  halogen  compound. 

317.  Benzophenone  exists  in  two  modifications :  one  is  unstable 
and  melts  at  27°;  the  other  is  stable  and  melts  at  49°. 

The  relation  of  these  substances  to  one  another  is  one  of  mano- 
tropy;  that  is,  at  all  temperatures  up  to  its  melting-point  the  meta- 
stable  form  changes  to  the  stable  form,  but  the  process  is  not 
reversible.  The  explanation  is  that  the  transition-point  of  the  two 
modifications  is  higher  than  the .  melting-point  of  the  metastable 
isomeride. 

For  a  substance  with  a  transition-point  (0),  the  vapour-pressure, 
'  p,  in  the  neighbourhood  of  this  point  is  represented  by  Fig.  78 


FIG.  78. — ENANTIOTROPIC 
SUBSTANCE." 


FIG.  79. — MONOTROPIC 
SUBSTANCE. 


("Inorganic  Chemistry,"  70).  AB  is  the  vapour-pressure  curve  of 
the  fused  substance.  Its  direction  must  be  such  that  on  the  right 
it  lies  lower  than  any  other  curve;  that  is,  it  must  be  nearest  to  the 
horizontal  axis.  Since  rise  of  temperature  ultimately  occasions  the 
fusion  of  all  solid  forms,  above  a  certain  temperature,  definite  for 
each  substance,  the  liquid  phase  must  be  the  most  stable;  in  other 
words,  it  must  have  the  lowest  vapour-pressure.  O/i  is  the  melting- 
point  of  the  metastable  modification,  which  is  higher  than  the 
transition-point:  Of>  is  that  of  the  stable  modification. 


§318]  KETONES  AND  OX1MES.  431 

AB  can,  however,  be  so  situated  that/!  and /,  are  below  0  (Fig. 
79).  Here  the  melting-point  is  lower  than  the  transition-point  0, 
so  that  the  latter  cannot  be  attained.  The  metastable  modification 
then  remains  in  the  metastable  state  up  to  its  melting-point,  the 
substance  being  monotropic.  In  the  more  usual  case  of  enantiotropy, 
on  rise  of  temperature  the  compound  first  attains  the  transition-point, 
then  undergoes  transformation,  and  finally  melts. 


Oximes. 

318.  Some  of  the  oximes  of  the  aromatic  aldehydes  and 
ketones  exhibit  a  peculiar  kind  of  isomerism.  Thus,  there  are 
two  isomerides  of  benzaldoxime :  benzantialdoxime  (a),  melting 
at  35°;  and  'benzsyualdoxime  (ft  or  iso),  which  melts  at  128°, 
and  on  treatment  with  acetic  anhydride  readily  loses  water, 
forming  benzonitrile: 

C6H5CJH 

|||         =C6H5.C=N+H20. 
N|OH 

With  acetic  anhydride,  the  anfo'aldoxime  yields  an  acetyl-derivative. 

It    has    been    proved    that    no    isomerides    of    the    ketoximes 
•p 
Tj,>C:NOH  exist,  when  R  and  R'  are  similar:  when  these  groups  * 

are  dissimilar,  two  isomerides  are  known.  Benzophenoneoxime 
and  its  derivatives  furnish  examples.  Despite  many  attempts  to 
prepare  an  isomeride,  benzophenoneoxime  is  known  in  only  one 
modification.  When,  however,  hydrogen  in  one  phenyl-group  is  sub- 
stituted, two  isomeric  oximes  can  be  obtained.  Monochlorobenzophe- 
none,  C6H5-CO-C6H4C1,  monobromobenzophenone,  C6H5.CO-C6H4Br. 
phenyltolylketone,  CH3'C6H4-CO'C6H5,  and  phenylanisylketone, 
CH3O-C6H4.CO-C6H5,  are  examples  of  ketones  which  yield  two 
isomeric  oximes.  Many  other  compounds  of  this  type  could  be 
cited. 

After  several  ineffectual  attempts  to  explain  such  isomerism 
by  the  ordinary  structural  formulae,  the  following  stereochemical 
explanation  of  the  observed  facts  has  been  adopted.  It  is  assumed 
that  the  three  affinities  of  the  N-atom  are  directed  towards  the 
angles  of  a  tetrahedron,  the  nitrogen  atom  itself  being  situated  at 
the  fourth  angle: 


432 


ORGANIC   CHEMISTRY. 
N 


[§318 


When  the  three  nitrogen  bonds  are  linked  to  carbon,  as  in  the 
nitriles,  the  following  spacial  representation  is  obtained: 


CH 


CH 


Stereoisomerism  is  here  impossible:  experience  has  shown  that 
none  of  the  numerous  nitriles  known  occurs  in  two  forms  due  to 
isomerism  in  the  CN-groups. 

When,  however,  the  nitrogen  atom  is  linked  to  carbon  by  two 
bonds,  two  isomeric  forms  become  possible: 


and 


These  can  be  more  readily  represented  by 

X— C— Y  X— C— Y 

II  and  ||        . 

N— Z  Z— N 

It  is  apparent  that  different  configurations  for  such  compounds 
are  only  obtained  when  X  and  Y  are  different,  since  when  they 
are  similar  the  figures  become  identical.  This  agrees  with  the 
facts  stated  at  the  beginning  of  this  section. 

It  can  also  be  determined  which  configuration  represents  each 
}      isomeride.     The  two  isomeric  benzaldoximes  have  the  formulas 


319]  OXIMES.  433 

06H5— C— H  C6H5— C— H 

and 
X— OH  HO— X 

BenzsT/rcaldoxime  Benzanft'aldoxime 

1.  11. 

In  formula  I.,  H  and  OH  are  nearer  together  than  in  formula  II. 
This  proximity  explains  the  facility  with  which  one  molecule  of 
water  is  eliminated  from  one  aldoxime  (syn),  and  not  from  the  other 
(anti).  On  this  account  configuration  I.  is  assigned  to  the  s?/naldox- 
ime,  and  configuration  II.  to  the  anfo'aldoxime. 

The  configuration  of  the  ketoximes  can  be  determined  by  the 
BECKMANN  transformation  (103),  as  is  made  clear  in  the  following 
example.  Two  isomeridesof  phenylanisylketoxime  are  known, 

CH30  •  C6H4— C— C6H5  CH30  •  C6H4— C— C6H5 

and 

N— OH  HO— N 

I.  II. 

the  first  melting  at  137°  and  the  second  at  116°.  By  the  BECKMANN 
transformation,  the  oxime  of  higher  melting-point  yields  the  anilide 
of  anisic  acid;  that  of  lower  melting-point,  the  aniside  of  benzoTc 
acid.  The  former  must  therefore  have  configuration  1.,  and  the 
second  configuration  II..  because  in  I.  the  groups  OH  and  C6H5  are 
adjacent,  and  exchange  places: 

CH30  •  C6H4— C— OH         CH30  •  C6H4— C=0 

N— C6H5  XH— C6H5' 

The  anilide  of  anisic  acid,  CH3O'C6H4-COOH,  is  thus  produced.  In 
II.,  anisyl  (CH3O  *C6H4 — )  and  OH  are  adjacent,  and  exchange  places, 
yielding  the  aniside  of  benzole  acid: 


HO— C— C6II5  O=C— C6H5 

CH3O  •  C6H4 — N  CH3O  •  C6II4— NH 


XI.     AROMATIC  PHOSPHORUS  AND  ARSENIC  DERIVATIVES, 

319.  Compounds  of  phosphorus  and  arsenic  with  aromatic  hydro- 
carbons, having  constituents  similar  to  those  of  the  nitro-com- 
pounds,  azo-compounds,  and  amino-compounds,  are  known. 

Phosphinobenzene,  C6H5'PO2,  cannot  be  obtained  analogously  to 
nitrobenzene,  by  the  interaction  of  metaphosphoric  acid  and  benzene. 


434 


ORGANIC  CHEMISTRY. 


[§319 


It  is  prepared  by  the  action  of  phenylphosphinic  acid  (79)  upon  its 
chloride  : 

CeH5.PO(OH)2+C6H5.POCl2  =  2C6H5-PO2+2HC1. 

Phenylphosphinic  Chloride 

acid 

It  is  a  white,  crystalline,  odourless  powder. 

Phenylphosphine,  C6H5'PH2,  is  obtained  by  distilling  phosphenyl 
chloride,  C6H5-PC12,  with  alcohol,  in  a  current  of  carbon  dioxide.  It 
is  a  liquid  of  very  penetrating  odour.  It  cannot  be  obtained  by  the 
reduction  of  phosphinobenzene. 

Phosphobenzene,  C6H5-P.:P-C6H5,  is  got  by  treating  phenyl- 
phosphine  with  phosphenyl  chloride  : 

•C6H5  -  CeH5-P:P-C6H5  +  2HCl. 

It  is  a  pale-yellow  powder,  insoluble  in  water,  alcohol,  and  ether.     It 
is  energetically  oxidized  by  weak  nitric  acid,  forming  phosphenylous 


acid,  OP-H      . 
\OH 

Phosphenyl  chloride,  C6H5-PC12,  the  starting-point  in  the  prepara- 
tion of  these  and  other  aromatic  phosphorus  derivatives,  can  be  pre- 
pared, as  can  its  homologues,  by  heating  aromatic  hydrocarbons 
with  phosphorus  trichloride  and  aluminium  chloride  under  a  reflux- 
condenser. 

Arsinobenzene,  C6H5'As02,  is  obtained  by  the  elimination  of 
water  from  phenylarsinic  acid,  C6H6'AsO(OH)2,  under  the  influence 
of  heat. 

Arsenobenzene,  CeHs'AslAs'CeHs,  is  formed  by  the  reduction  of 
phenylarsine  oxide,  C6H6-AsO,  with  phosphorous  acid.  It  forms 
yellow  needles,  and  is  converted  by  oxidation  into  phenylarsinic 
acid,  C6H6-AsO(OH)2. 

Other  aromatic  arsenic  derivatives  are  mentioned  in  339. 

The  following  series  of  compounds  are  known: 


Nitrobenzene 

C6H6-P02 

Phosphinobenzene 


C  eHs  •  rs  2  •  C  6-H.5 

Azobenzene 


Phosphobenzene 


C6H5.NH2 

Phenylamine 

C6H5.PH2 

Phenylphosphine 


C6H5.As02 

rArsinobenzene 


Arsenobenzene 


Although    these    compounds   have    analogous    formulae,   both    the 
methods  employed  in  the  preparation  of  the  individual  members 


320]  AROMATIC  METALLIC  COMPOUNDS.  435 

of   each  series,  and  the   properties  of  the   individuals  themselves, 
exhibit  wide  divergences. 


XH.   AROMATIC  METALLIC  COMPOUNDS. 

320.  Mercury,  tin,  lead,  and  magnesium  are  the  only  metals 
which  yield  aromatic  compounds:  they  are  much  less  important 
than  the  metallic  compounds  of  the  aliphatic  series.  Mercury 
phenide,  Hg(C6H6)2,  is  obtained  by  the  action  of  sodium-amalgam 
upon  bromobenzene.  It  is  crystalline,  and  resembles  the  corre- 
sponding alkyl-derivatives  in  its  stability  towards  atmospheric 
oxygen.  When  its  vapour  is  passed  through  a  red-hot  tube,  it 
decomposes  into  mercury  and  diphenyl  (371):  the  same  effect  is 
partially  produced  by  distillation.  When  mercury  acetate  is  heated 
with  benzene  at  110°,  there  results  phenylmercury  acetate, 
CeHs'Hg'OOOCHs,  the  acetic-acid  salt  of  the  base  phenylmercury 
hydroxide,  C6H5'Hg'OH.  The  homologues  of  benzene,  nitro- 
benzene, and  other  substances  yield  analogous  compounds. 

Aromatic  magnesium  compounds  are  referred  to  in  289. 


BENZENE    HOMOLOGUES    WITH    SUBSTITUTED    SIDE- 
CHAINS. 

321.  The  introduction  of  a  substituent  into  a  homologue 
of  benzene  can  take  place  not  only  in  the  nucleus,  but  also  in 
the  side-chain.  The  second  type  of  substitution  has  been 
exhaustively  investigated  for  the  toluene  derivatives  with 
hydrogen  of  the  methyl-group  replaced  by  various  substituents. 
These  substances  are  to  be  regarded  as  methane  with  one  hydrogen 
atom  replaced  by  phenyl,  and  one  or  more  of  the  other  hydrogen 
atoms  exchanged  for  a  corresponding  number  of  atoms  or  radicals. 
A  close  approximation  between  the  properties  of  these  compounds 
and  those  of  the  corresponding  aliphatic  derivatives  would  be 
anticipated,  and  this  view  finds  abundant  confirmation  in  the 
facts  recorded  in  this  chapter. 

I.  COMPOUNDS  WITH  HALOGEN  IN  THE  SIDE-CHAIN. 

In  the  interaction  of  chlorine  or  bromine  with  toluene,  the 
entrance  of  the  halogen  into  the  nucleus  or  into  the  side-chain 
is  determined  by  the  experimental  conditions.  Compounds 
of  the  type  X-CeH^CH^  are  called  halogen-toluenes,  and  those 
of  the  formula  Cells -CH2X  benzyl  halides.  A  summary  of  the 
influence  exerted  by  the  experimental  conditions  is  subjoined. 

1.  Temperature. — At  low  temperatures,  halogens  substitute  in 
the  nucleus,  and  at  high  temperatures,  in  the  side-chain :  thus,  on 
treatment  with  chlorine,  cold  toluene  yields  o-chlorotoluene  and 
p-chlorotoluene;    when,  however,  chlorine  or  bromine  is  brought 
into     contact     with    boiling    toluene     (110°),     benzyl     chloride, 
C6H5'CH2C1,  or  benzyl  bromide,  C6H5-CH2Br,  is  almost  exclusively 
formed. 

2.  Sunlight. — A  striking  example  of  the  influence  of  light  is 
furnished  by  the  dark-brown  mixture  of  toluene  and  bromine. 
At  ordinary  temperature  in  absence  of  light,  interaction  is  very 
slow,  an  interval  of  many  days  being  necessary  for  the  complete 

436 


§321]  HALOGEN ATION  OF  TOLUENE.  437 

disappearance  of  the  bromine,  with  formation  of  hydrogen 
bromide  and  bromotoluenes.  On  exposing  the  mixture  to 
daylight,  it  becomes  decolorized  in  a  few  minutes,  the  brpmine 
entering  the  side-chain  only. 

jlany  instances  of  the  influence  of  light  on  chemical  reactions 
have  been  observed.  They  include  the  intramolecular  rearrange- 
ment of  atoms  and  groups,  the  acceleration  of  reactions,  and,  as 
in  the  example  just  cited,  the  formation  of  compounds  entirely 
different  from  those  formed  in  absence  of  light. 

3.  Concentration. — The  proportion  of  halogen  to  toluene  has 
an  important  influence.     At  50°  in  absence  of  light,  the  product 
obtained  by  the  interaction  of  bromine  and  toluene  in  the  molec- 
ular ratio  1:4-26  contains  24-1  per  cent,   of  benzyl  bromide, 
but  in  the  ratio  1  :  28-55  it  has  95-3  percent,  of  this  substance. 

4.  Catalysts. — Aluminium  or  ferric  halides  have  a  very  power- 
ful  catalytic   action.     So  small  a  proportion  of  ferric  bromide 
as  0-002  gramme-molecule  to  each  gramme-molecule  of  bromine 
completely  over-rides  all  other  influences,   causing  substitution 
in  the  nucleus  only,  quite  irrespective  of  the  reaction  being  carried 
on  in  the  presence  of  light,  at  high  temperature,  or  at  different 
concentrations. 

The  benzyl  halides,  C6H5-CH2X,  are  readily  distinguished 
from  the  isomeric  halogen  derivatives  of  toluene.  In  the  first 
place,  their  halogen  atoms  display  the  same  aptitude  for  reactions 
involving  double  decomposition  as  those  of  the  alkyl  halides, 
but  the  halogen  atoms  of  the  isomeric  halogen-toluenes  are  as 
firmly  linked  as  those  in  the  monohalogen-benzenes.  In  the 
second  place,  the  benzyl  halides  are  converted  by  oxidation 
into  benzoic  acid,  C6H5-COOH,  but  the  halogen-toluenes  into 
halogen-benzoiic  acids,  C6H4X-COOH.  In  the  third  place,  the 
halogen-toluenes  are  characterized  by  their  faint,  but  not  dis- 
agreeable, odour;  but  the  benzyl  halides  have  a  most  irritating 
effect  on  the  mucous  membrane  of  the  eyes,  a  property  specially 
noticeable  in  benzyl  iodide. 

Benzyl  chloride  is  a  colourless  liquid  of  stupefying  odour, 
intensified  by  warming:  it  boils  at  178°,  and  has  a  specific  gravity 
of  1-113  at  15°.  Benzyl  bromide  is  also  a  colourless  liquid. 
Benzyl  iodide  is  prepared  by  heating  benzyl  chloride  with  potas- 
sium iodide:  it  melts  at  24°,  and  decomposes  when  boiled.  It 


438  ORGANIC  CHEMISTRY.  [§  322 

has  a  powerful  and  unbearably  irritating  odour,  productive  of 
tears. 

The  prolonged  action  of  chlorine   on  boiling  toluene  yields 
benzol    chloride,    C6H5«CHC12,    and    benzotrichloride,    Cells- CC13. 

II.   PHENYLNITROMETHANE  AND  THE  PSEUDO-ACIDS. 

322.  Phenylnitromethane,  C6H6*CH2N02,  is  an  aromatic  com- 
pound with  a  nitro-group  in  the  side-chain,  as  is  evident  from  its 
formation  by  the  action  of  benzyl  chloride  or  iodide  on  silver  nitrite: 

=  C6H5-CH2N02+AgCl. 

It  can  be  reduced  to  benzylamine,  which  proves  it  to  be  a  true  nitro- 
compound.  Phenylnitromethane,  and  its  derivatives  with  substitu- 
ents  attached  to  the  nucleus,  exist  in  two  tautomeric  modifications 
readily  transformed  into  each  other.  Phenylnitromethane  is  a 
liquid:  its  aqueous  solution  does  not  react  with  ferric  chloride. 
After  it  has  been  converted  into  its  sodium  derivative  by  the  action 
of  sodium  alkoxide,  addition  of  excess  of  a  strong  mineral  acid  causes 
the  separation  of  a  crystalline  substance  of  the  same  composition  as 
Phenylnitromethane :  the  aqueous  solution  of  this  compound  gives  a 
coloration  with  ferric  chloride.  On  standing  for  some  hours,  these 
crystals  are  completely  reconverted  into  the  ordinary  liquid  phenyl- 
nitromethane.  It  is  very  probable  that  the  sodium  compound  and 
the  unstable  modification  corresponding  with  it  have  the  constitutions 

C6H6-CH:NO-ONa,     and    C6H5-CH:NO-OH. 

The  presence  of  a  hydroxyl-group  is  proved  by  the  formation  of 
dibenzhydroxamic  acid  on  treatment  with  benzoyl  chloride : 


/ 
C6H5-CH:Nf         +C10C.C6H5  -»  C6H6-CH:Nf 

XONa  X0-OOC6H6 

Sodiophenyh'so- 
nitromethane 

-»  C6H6-CO— N— O-OOCeHe. 
H 

Dibenzhydroxamic  acid 

Another  proof  of  the  presence  of  a  hydroxyl-group  is  that  isonitro- 
compounds,  unlike  ordinary  nitro-compounds,  react  vigorously  with 
phenyl  ?'socyanate  at  low  temperatures. 


§  323]  PSEUDO-ACIDS.  439 

From  these  facts  it  may  be  inferred  that  when  phenylnitro- 
methane,  C6H5 -CHiXC^is  converted  into  a  salt,  it  first  changes  to 
an  isomeric  modification.  Inversely,  when  it  is  liberated  from  its 
sodium  compound,  the  {so-modification,  or  aa'-modification,  is  first 
produced,  and  slowly  changes  to  the  ordinary  form. 

The  dilute  aqueous  solution  of  m-nitrophenylnitromethane  affords 
a  striking  example  of  this  phenomenon.  This  compound  is  colour- 
less, but  its  sodium  salt  has  a  deep-yellow  colour.  On  the  addition 
of  an  equivalent  quantity  of  hydrochloric  acid  to  its  deeply-tinted 
solution,  the  yellow  colour  disappears  somewhat  slowly,  indicating 
the  conversion  of  the  zso-compound  into  its  normal  isomeride. 

The  discharge  of  the  colour  is  attended  by  another  phenomenon : 
the  electric  conductivity  of  the  liquid  is  considerably  greater  imme- 
diately after  the  addition  of  the  hydrochloric  acid  than  it  is  several 
minutes  later,  when  the  colour  has  nearly  vanished.  The  explana- 
tion of  this  is  that  the  iso-form  is  a  true  acid,  and  is  therefore  a 
•  conductor  in  aqueous  solution,  while  the  solution  of  the  normal  modi- 
fication is  a  non-conductor,  and  therefore  possesses  no  acidic  character. 

Compounds  which  change  to  an  act-modification  on  formation  of 
metallic  derivatives  are  called  pseudo-acids.  In  addition  to  phenyl- 
nitromethane  and  its  ring-substituted  derivatives,  other  pseudo-acids 
are  known,  most  of  which  were  prepared  by  HANTZSCH. 

323.  Besides  the  properties  indicated  above,  the  pseudo-acids 
possess  others  by  which  they  may  be  detected.  It  has  just  been 
stated  that  the  addition  of  a  strong  acid  to  a  pseudo-acid  salt  liberates 
the  aci-form,  which  is  slowly  converted  into  the  normal  modification. 
Inversely,  the  addition  of  an  equivalent  quantity  of  caustic  alkali  to 
the  normal  modification  results  in  its  gradual  neutralization.  This 
"  slow  neutralization  "  is  a  characteristic  of  the  pseudo-acids. 

Another  of  the  characteristics  by  which  they  may  be  recognized 
is  illustrated  by  dinitroethane,  which,  after  being  liberated  from  its 
sodium  salt  in  accordance  with  the  equation 

/N02  .N02 

CH3-(X  +  HC1  =  CH3-C<;  +NaCl, 

vNO-ONa  XNO-OH 

aci-Dinitroethane 

is  so  rapidly  converted  into  the  normal  compound,  CH3-CH<^Q2, 

that  a  change  in  the  electric  conductivity  of  the  solution  can  scarcely 
be  observed  even  at  0°.  The  neutral  reaction  of  the  alkali-metal 
derivatives  of  the  non-conducting  or  weakly-conducting  hydrogen 
compound  nevertheless  indicates  the  existence  of  a  pseudo-acid.  An 


440  ORGANIC  CHEMISTRY.  [§  324 

acid  which  is  so  weak  that  its  solution  is  a  bad  conductor  of  elec- 
tricity yields  alkali-metal  salts  which  undergo  strong  hydrolytic 
dissociation,  and  therefore  have  a  strongly  alkaline  reaction 
("Inorganic  Chemistry,"  65).  Such  a  substance  as  sodiodinitroe- 
thane  forms  a  non-alkaline  solution,  arid  must  therefore  be  derived 
from  an  acid  other  than  dini  troethane,  since  this  substance  has  a 
neutral  reaction  and  is  a  non-conductor  in  aqueous  solution. 

The  difference  in  structure  between  the  salt  of  a  pseudo-acid 
and  the  free  acid  can  also  be  detected  by  their  refraction.  Compar- 
ison of  the  molecular  refraction  of  an  aqueous  or  alcoholic  solution 
of  an  acid  with  that  of  its  sodium  salt  reveals  a  constant  difference, 
even  for  weak  acids.  For  a  solution  in  the  equivalent  quantity 
of  caustic  alkali  of  a  nitro-compound  which  yields  a  pseudo-acid , 
the  difference  between  the  molecular  refraction  of  the  acid  and  that 
of  the  salt  formed  is  much  greater.  This  phenomenon  indicates 
the  transformation  of  the  pseudo-acid  into  its  aci-form  to  be  an 
intermediate  process  preceding  the  formation  of  the  salt. 

III.  ACIDS  WITH  CARBOXYL  IN  THE  SIDE-CHAIN. 

324.  One  of  the  compounds  with  a  saturated  side-chain 
is  phenylacetic  acid,  C6H5-CH2-COOH.  It  is  prepared  by  the 
interaction  of  potassium  cyanide  and  benzyl  chloride,  followed  by 
hydrolysis  of  the  resulting  nitrile,  benzyl  cyanide,  Cells -CH^-CN. 
Phenylacetic  acid  melts  at  76°,  and  is  converted  by  oxidation. 

PTT 

into  benzole  acid ;  whereas  the  isomeric  toluic  acids,  C6H4  <QQQ  jj> 

are  transformed  by  oxidation  into  the  dibasic  phthalic  acids. 

Mandelic  acid  has  both  hydroxyl  and  carboxyl  in  the  side- 
chain.  Its  constitution  is  CeHs-CHOH-COOH,  as  its  synthesis 
from  benzaldehyde  and  hydrocyanic  acid  indicates.  In  this 
reaction  manddonitnle,  C6H5»CHOH»CN,  is  an  intermediate 
product.  Addition  of  quinine  to  the  mixture  of  benzaldehyde 
and  hydrocyanic  acid  makes  the  synthesis  asymmetric,  so  that 
an  optically  active  mandelonitrile  is  formed.  The  quinine 
functions  as  an  optically  active  catalyst,  its  action  being  similar 
to  that  exerted  by  the  enzyme  emulsin.  The  mandelic  acid  found 
in  nature  is  Isevo-rotatory.  The  synthetical  acid  can  be  resolved 
by  the  action  of  cultures  obtained  from  mildew  (Penicillium 
glaucum),  the  dextro-rotatory  acid  being  left  intact.  The 


§§  325,  326]      BENZYL  ALCOHOL   AND  BENZYLAMINE.  441 

decomposition  is  also  effected  by  the  formation  of  the  cinchonine 
salts,  when  the  salt  of  the  dextro-rotatory  acid  crystallizes  out 
first. 

Inactive  mandelic  acid  is  also  called  "  para-mandelic  acid."  It 
melts  at  119°,  and  dissolves  very  readily  in  water:  the  optically 
active  modification  melts  at  134°,  and  is  less  soluble  in  water. 


IV.  AROMATIC  ALCOHOLS. 


325.  Benzyl  alcohol,  CeHs-CH^OH,  is  the  typical  aromatic 
alcohol  it  possesses  nearly  all  the  properties  of  an  aliphatic 
alcohol,  It  can  be  obtained  by  -treatment  of  benzyl  chloride 
with  potassium  acetate,  and  saponification  of  the  ester  of  acetic 
acid  thus  formed.  It  can  also  be  prepared  by  electro-reduction 
of  benzoi'c  acid  in  sulphuric  -acid  solution  with  lead  cathodes.  It 
reacts  readily  with  phosphorus  pentachloride,  yielding  benzyl 
chloride,  and  forms  esters,  ethers,  etc.:  being  a  primary  alco- 
hol, it  can  be  oxidized  to  the  corresponding  aldehyde,  benzaldehijde 
(314),  and  also  to  benzole  acid  (312).  It  differs  from  the  aliphatic 
alcohols  in  its  behaviour  towards  sulphuric  acid,  which  causes 
resinification,  instead  of  the  formation  of  the  corresponding 
sulphuric  ester.  Benzyl  alcohol  possesses  no  phenolic  properties: 
it  is  insoluble  in  alkalis,  and  does  not  yield  the  characteristic 
phenol  coloration  with  ferric  chloride. 

Benzyl  alcohol  is  a  liquid  which  dissolves  with  difficulty  in 
water  :  it  boils  at  206°,  and  possesses  only  a  faint  odour. 

V.    COMPOUNDS  WITH  THE  AMINO-GROUP  IN  THE  SIDE-CHAIN. 


326.  Benzyl  amine,  CeHs'CH^'NH^,  is  a  type  of  the  amines 
with  XH2  in  the  side-chain.  It  can  be  obtained  by  the  various 
methods  employed  in  the  preparation  of  aliphatic  amines,  such  as 
the  action  of  benzyl  chloride  upon  ammonia,  by  which  dibenzyl- 
amine  and  tribenzylamine  are  also  formed  ;  the  addition  of  hydrogen 
to  benzonitrile,  CeHs-CN;  the  reduction  of  phenylnitromethane, 
Cells  -CH2-NO2;  and  so  on.  The  method  for  its  formation  and 
its  properties  prove  that  benzylamine  belongs  to  the  primary 
amines  of  the  aliphatic  series:  thus,  it  does  not  yield  diazonium 


442  ORGANIC  CHEMISTRY.  [§326 

compounds;  and  its  aqueous  solution  has  a  strongly  alkaline 
reaction,  proving  it  to  be  a  much  stronger  base  than  aniline,  in 
which  the  NH2-group  is  under  the  direct  influence  of  the  phenyl- 
group. 

Benzylamine  is  a  liquid  of  ammoniacal  odour:  it  boils  at  185°, 
is  volatile  with  steam,  and  has  a  specific  gravity  of  0-983  at  19°. 
It  absorbs  carbon  dioxide  from  the  air. 


COMPOUNDS    CONTAINING   AN    UNSATURATED    SIDE- 

CHAIN. 

Hydrocarbons. 

327.  Styrole,  C6H5'CH:CH2,  is  a  coal-tar  product,  and  derives  its 
name  from  its  occurrence  in  storax.  It  can  be  obtained  from  cinnamic 
acid,  C6H5'CH:CH'COOH,  by  heating  it,  whereupon  carbon  dioxide 
is  eliminated.  It  is  a  liquid  of  agreeable  odour,  and  boils  at  146°. 
Heating  converts  it  into  a  vitreous  mass  called  metastyrole,  a  poly- 
meride  of  unknown  molecular  weight,  the  same  transformation 
taking  place  slowly  at  ordinary  temperature.  Like  other  substances 
with  a  double  iinking,  styrole  has  the  power  of  forming  addition- 
products.  On  treatment  with  nitric  acid,  it  yields  nitrostyrole, 
C6H5'CH:CH*N02,  with  the  nitro-group  in  the  side-chain.  The 
constitution  of  this  compound  follows  from  its  formation  by  the 
condensation  of  benzaldehyde  with  mtromethane,  under  the  catalytic 
influence  of  alcoholic  potash: 

H  _ 
C6H5-C[OTH^CH-N02  -  C6H5.CH:CH-NO2  +  H2O. 

Phenylacetylene,  C6H5-C=CH,  can  be  obtained  by  treating 
acetophenone  with  phosphorus  pentachloride,  and  acting  on  the 
resulting  compound,  C6H5  •  CC12  •  CH3,  with  caustic  potash;  or  from 
phenylpropiolic  acid,  C6H5-C:'OCOOH,  by  heating  its  cupric  salt 
with  water.  In  many  respects  it  resembles  acetylene  ;  for  example, 
it  yields  metallic  derivatives.  On  solution  in  concentrated  sulphuric 
acid,  it  takes  up  one  molecule  of  water,  forming  acetophenone. 


Alcohols  and  Aldehydes. 

Cinnamyl  alcohol,  C6H6-CH:CH-CH2OH,  is  the  only  repre- 
sentative of  the  unsaturated  alcohols  which  need  be  mentioned.  It 
is  a  crystalline  substance  with  an  odour  of  hyacinths,  and  is  present 

443 


444  ORGANIC  CHEMISTRY.  [§328 

as  an  ester  in  storax.  Careful  oxidation  converts  it  into  cinnamic 
acid  (328),  and  more  vigorous  oxidation  into  berizoic  acid. 

TT 

Cinnamaldehyde,   C6H6-CH  :CH'C0,    is  the  chief  constituent 

of  oil  of  cinnamon,  from  which  it  can  be  obtained  by  means  of  its 
sulphite  compound.  It  is  an  oil  of  agreeable  odour,  and  boils  at 
246°.  It  is  resinified  by  strong  acids,  and  with  ammonia  yields 
hydrocinnamide,  NaCCcHtQJIs)!,  analogous  to  hydrobenzamide(3i5). 

Acids. 

328.  Cinnamic  acid,  C6H5-CH:CH.COOH,  is  the  most  im- 
portant unsaturated  acid.  It  is  present  in  some  balsams,  and  in 
storax.  It  is  manufactured  by  a  synthetic  method  discovered  by 
SIR  WILLIAM  PERKIN.  Benzaldehyde  is  heated  with  acetic  anhy- 
dride, in  presence  of  sodium  acetate  as  a  catalyst: 


Benzaldehyde  Acetic  anhydride 

+H2O  =  C6H5.CH:CH.COOH+HO.CO.CH3. 

Cinnamic  acid  Acetic  acid 

PERKIN'S  synthesis  can  be  carried  out  with  substituted  benz- 
aldehydes  on  the  one  hand,  and  with  homologues  of  acetic  acid  or 
with  dibasic  acids  on  the  other,  so  that  it  is  possible  to  obtain  a 
great  number  of  unsaturated  aromatic  acids  by  its  aid. 

Cinnamic  acid  can  also  be  got  by  the  action  of  benzal  chloride 
(321),  C6H5-CHC12,  upon  sodium  acetate.  It  can  further  be  synthe- 
sized by  the  condensation  of  malonic  acid  with  benzaldehyde,  which 
takes  place  readily  under  the  catalytic  influence  of  ammonia,  one 
molecule  of  carbon  dioxide  being  eliminated: 

=  C6H5.CH:CH-COOH+C02+H20. 

Malonic  acid 

Cinnamic  acid  is  a  crystalline  substance,  melts  at  134°,  and  dis- 
solves with  difficulty  in  cold  water.  In  all  respects  it  possesses  the 
character  of  a  substance  with  a  double  bond,  and  therefore  forms 
addition-products  and  reduces  VON  BAEYER'S  reagent  (113). 

Its  constitution  indicates  that  two  stereoisomerides  are  possible: 

• 

Cells  —  C  —  H  CeHs  —  C  —  H 

II  and  ||        . 

H—  C—  COOH  COOH—  C—  H 


328]  CINNAMIC  ACID.  445 

Four  modifications,  however,  are  known:  ordinary  cinnamic  acid; 
allocinnamic  acid,  melting  at  68°;  and  two  isocinnamic  acids,  melting 
at  58°  and  42°  respectively.  BIILMANN  has  proved  that  the  last 
three  acids  are  modifications  of  a  single  form,  and  therefore  afford 
an  example  of  trimorphism.  On  inoculating  the  liquid,  obtained  by 
fusion  of  any  of  them,  with  one  of  the  forms,  that  form  crystallizes 
out.  A/focinnamic  acid  and  the  isocinnamic  acids  can  be  prepared 
by  partial  reduction  of  phenylpropiolic  acid,  C6H5'C^OCOOH 
(327);  and  must,  therefore,  have  the  ci's-configuration  (I.),  as  is 
evident  from  a  model.  It  follows  that  ordinary  cinnamic  acid  has 
the  £rems-configuration  (II) : 

H-OCeHs  C6H6-C-H 

I.        II  J  II.  || 

H-OCOOH  H-OCOOH 

Cis  Trans 

It  can  be  converted  into  the  crs-form  by  exposing  its  solution  in 
benzene  to  the  ultraviolet  rays  of  a  "uviol"  lamp  for  ten  days. 


POLYSUBSTITUTED  BENZENE  DERIVATIVES. 

329.  A  great  number  of  polysubstituted  derivatives  of  benzene 
is  known,  but  only  a  few  of  special  theoretical  or  technical 
interest  will  be  considered.  For  the  sake  of  systematic  treat- 
ment, the  substitution-products  will  be  taken  in  the  same  order 
as  has  been  adopted  in  the  preceding  pages  for  the  monosub- 
stituted  derivatives.  The  polyhalogen  compounds  will  be  dis- 
cussed first,  then  the  substituted  nitrobenzenes,  sulphonic  acids, 
phenols,  and  so  on. 

The  general  rule  holds  that  substituents  simultaneously  present 
exercise  their  normal  functions,  although  the  effect  of  a  given 
substituent  is  also  often  greatly  modified  by  the  presence  of  -the 
other  atoms  or  groups. 

I.   POLYHALOGEN  DERIVATIVES. 

The  polyhalogen  derivatives  can  be  prepared  by  the  direct 
action  of  chlorine  or  bromine  on  the  aromatic  hydrocarbons  in 
presence  of  a  catalyst,  the  anhydrous  ferric  halides  being  specially 
suitable  for  this  purpose.  The  mode  of  procedure  is  to  introduce 
a  small  proportion  of  dry  iron-powder  into  the  liquid,  and  pass 
in  chlorine  or  add  bromine  drop  by  drop.  If  a  halogen  atom  is 
already  attached  to  the  nucleus,  replacement  takes  place  mainly 
at  the  para-position,  but  the  or^o-compound  and  a  small  pro- 
portion of  the  m^a-compound  are  simultaneously  formed. 
m-Dichlorobenzene  and  m-dibromobenzene  can  be  prepared  by 
reduction  of  m-dimtrobenzene  (331),  and  subsequent  diazotiza- 
tion  of  the  product.  The  para-dihalogen  compounds  are  solid, 
the  isomeric  or^o-compounds  and  we£a-compounds  are  liquid. 
When  three  halogen  atoms  enter  the  nucleus,  the  main  product 
is  the  l:2:4-trihalogenbenzene, 

X 


446 


§  330J  POLYSUBSTITUTED  DERIVATIVES.  447 

since  the  same  product  is  obtained  from  each  of  the  three 
dihalogenbenzenes.  Prolonged  chlorination  of  benzene  sub- 
stitutes its  six  hydrogen  atoms,  with  formation  of  JULIN'S  chloro- 
carbon,  C6Cl6,  colourless  needles  melting  at  229°.  It  is  very 
stable,  soluble  with  difficulty  in  most  solvents,  and  is  often  a 
product  of  the  energetic  chlorination  of  various  benzene  deriv- 
atives, the  substituents  already  present  being  displaced  by 
chlorine. 

II.  HALOGEN-NITRO-COMPOUNDS. 

330.  Nitration  of  a  monohalogenbenzene  yields  only  the  ortho- 
compound  and  the  para-compound,  the  second  being  formed  in 
larger  proportion.  An  example  is  furnished  by  the  nitration  of 
monochlorobenzene;  at  ordinary  temperature  the  product  con- 
sists of  about  70  per  cent,  of  p-chloronitrobenzene,  and  about  30 
percent,  of  o-chloronitrobenzene,  Cl-CefU-NC^.  m-Chloronitroben- 
zene  is  readily  prepared  by  chlorination  at  elevated  temperature 
of  a  mixture  of  nitrobenzene  with  20  per  cent,  of  its  weight  of 
antimony  pentachloride.  m-Halogen-nitrobenzenes  can  also  be 
prepared  from  m-nitroaniline  by  the  diazotization-method. 

Unlike  the  halogen  in  the  monohalogenbenzenes,  that  in  the 
p-halogen-nitrobenzenes  and  the  o-halogen-nitrobenzenes  is  char- 
acterized by  its  power  of  taking  part  in  double  decompositions. 
When  these  substances  are  heated  with  an  alcoholic  solution  of 
sodium  methoxide,  the  halogen  atom  is  replaced  by  OCH3;  with 
alcoholic  ammonia  the  halogen  atom  is  exchanged  for  NH2.  A 
contrast  is  presented  by  the  m-halogen-nitrobenzenes,  their 
halogen  being  almost  as  difficult  to  replace  as  that  in  the  unsub- 
stituted  monohalogenbenzenes. 

The  presence  of  several  nitro-groups  in  the  nucleus  at  the 
ortfio-position  and  the  para-position  to  halogen  causes  a  marked 
increase  in  the  adaptability  for  double  decomposition.  The 
Cl-atom  in  picryl  chloride, 

Cl 
N02/\N02 


NO2 
is  replaceable  by  a  great  variety  of  substituents.     This  substance 


448  ORGANIC  CHEMISTRY.  [§  331 

has  the  character  of  an  acid  chloride,  being  converted  by  hot, 
water  into  hydrogen   chloride  and    picric  acid, 

and  by  ammonia  into  picramide,  CeH^g  ~  '   • 


III.   POLYNITRO-DERIVATIVES. 

331.  m-Dinitrobenzene  is  obtained  by  the  nitration  of  benzene 
with  a  mixture  of  concentrated  sulphuric  acid  and  faming  nitric 
acid.  It  forms  colourless  needles  melting  at  90°.  On  reduction,  it 
yields  m-phenylenediamine,  and  is  therefore  employed  in  the  prepa- 
ration of  coal-tar  dyes :  it  is  also  used  in  the  manufacture  of  explo- 
sives, since  it  can  be  exploded  by  mercury  fulminate.  In  addition 
to  the  w-compound,  small  quantities  of  o-dinitrobenzene  and  traces 
of  p-dinitrobenzene  are  formed.  Stronger  nitration,  effected  by  a 
mixture  of  nitric  acid  and  fuming  sulphuric  acid  heated  to  140°, 
converts  m-dinitrobenzene  into  symmetrical  trinitrobenzene  (1:3:5), 
which  melts  at  121°. 

The  hydrogen  atoms  and  nitro-groups  in  the  polynitrobenzenes 
are  much  more  readily  replaced  than  those  in  mononitrobenzene. 
Thus,  m-dinitrobenzene  is  converted  by  oxidation  into  2:6- 
dinitrophenol,  and  l:3:5-trinitrobenzene  into  2 : 4 : 6-trinitro- 
phenol,  or  picric  acid: 

N02  N02 

+  NO2/~~\OH. 

NO2  NO2 

By  the  action  of  sodium  ethoxide  and  methoxide  respectively 
one  of  the  nitro-groups  in  o-dinitrobenzene  and  p-dinitrobenzene 
can  be  replaced  by  OC2H5  and  OCH3: 


It  is  remarkable  that  this  substitution  does  not  take  place  with 
m-dinitrobenzene,  although  in  l:3:5-trinitrobenzene,  with  each 
of  its  substituents  in  the  meta-position  to  the  other  two,  one  of 


§  332]  POLYSUBSTITUTED  DERIVATIVES.  449 

the  nitro-groupa  can  be  readily  replaced  by  OCH3  ("  Laboratory 
Manual/' XXXIII,  3). 

When  boiled  with  sodium  hydroxide,  o-dinitrobenzene  yields 
o-nitrophenol ,  and  when  heated  with  alcoholic  ammonia,  o-nitro- 
aniline: 


JNO2l  +  NaOH  / 

C6H4<  =  C6H4<          +NaN02. 

\\O2  2  \NO2 


±  . 

It  has  not  been  possible  to  introduce  more  than  three  nitro- 
groups  into  benzene  by  direct  nitration,  substitution  even  by  the 
third  nitro-group  meeting  with  considerable  opposition.  The 
homologues  of  benzene  are  much  more  readily  converted  into  their 
higher  nitro-derivatives  than  benzene  itself. 

Trinitrobutylxylene,  containing  a  tertiary  butyl-group,  has  a  power- 
ful odour  resembling  that  of  musk.  It  is  a  perfume,  and  is  called 
" artificial  musk." 

IV.    SUBSTITUTED  BENZENESULPHONIC  ACIDS. 

332.  Digestion  of  monochlorobenzene  or  monobromobenzene 
with  concentrated,  or  better  fuming,  sulphuric  acid  yields  exclu- 
sively p-chlorobenzenesulphonic  acid  or  p-bromobenzenesulphonic 
acid.  The  properties  of  these  substances  approximate  closely  to 
those  of  the  unsubstituted  benzenesulphonic  acid. 

On  fusion  with  potassium  hydroxide,  each  of  the  three  bromoben- 

OTT  1 

zenesulphonic  acids  is  converted  into  resorcinol,  C6H4<QTTo>oneof 

the  few  instances  of  substitution  at  a  position  other  than  that  occu- 
pied by  the  group  replaced.  Additional  examples  of  the  same 
phenomenon  will  be  mentioned  subsequently  (333). 

Both  nitration  of  benzenesulphonic  acid  and  sulphonation'of 
nitrobenzene  yield  chiefly  m-nifrobenzenesulphonic  acid,  with 
simultaneous  production  of  a  small  percentage  of  the  isomeric 
ortho-compound  and  p&ra,-compound. 

When  benzene  and  its  homologues  are  heated  at  a  high  tem- 
perature with  fuming  sulphuric  acid,  disulphonic  acids  and  tri* 


450  ORGANIC  CHEMISTRY.  [§333 

sulphonic  acids  are  produced,  but  it  has  not  been  found  possible 
to  introduce  more  than  three  sulpho-groups.  Addition  of  silver 
sulphate  greatly  facilitates  the  formation  of  benzenetrisulphonic 
acid.  With  respect  to  the  production  of  disulphonic  acids, 
benzene  yields  chiefly  benzene-m-disulphonic  acid,  a  substance 
partially  converted  into  benzene-p-disulphonic  acid  by  prolonged 
heating  at  a  high  temperature  with  sulphuric  acid.  Inversely, 
under  the  same  conditions  the  para-compound  is  partially  trans- 
formed into  benzene-m-disulphonic  acid.  Benzene-o-disulphonic 
acid  is  not  produced  by  direct  sulphonation  of  benzene. 

V.   SUBSTITUTED  PHENOLS  AND  POLYHYDRIC  PHENOLS. 
Halogenphenols. 

333.  The  direct  action  of  cKlorine  or  bromine  on  phenol 
yields  o-chlorophenol  and  p-chlorophenol,  or  o-bromophenol  and 
p-bromophenol.  These  compounds  are  also  formed  by  reduction 
of  the  halogen-nitrobenzenes,  with  subsequent  diazotization  of 
the  products.  In  aqueous  solution  the  halogenation  is  not  limited 
to  the  entrance  of  one  halogen  atom,  but  yields  higher  products,  an 
example  being  the  precipitation  of  2:4:6-tribromophenol  by  add- 
ing bromine-water  at  ordinary  temperature  to  an  aqueous  solution 
of  phenol  (293).  The  or^o-compounds  have  a  pungent,  very 
penetrating  odour.  At  ordinary  temperature,  the  or^o-isomerides 
and  wda-isomerides  of  the  chlorophenols  and  bromophenols 
are  liquid;  the  para-isomerides  are  solid  (288).  Fusion  with 
potassium  hydroxide  replaces  their  halogen  by  hydroxyl,  although 
the  corresponding  hydroxy -derivative  is  not  always  formed  (332). 
The  acidic  character  of  the  phenols  is  considerably  strengthened 
by  the  introduction  of  halogen,  exemplified  by  the  power  of 
trichlorophenol  to  decompose  carbonates. 

Iodine  can  substitute  hydrogen  in  phenol  only  in  presence  of 
an  oxidizer,  the  hydrogen  iodide  being  oxidized,  and  thus  pre- 
vented from  eliminating  the  iodine  atom  from  the  iodophenol. 

Nitrophenols. 

The  increased  aptitude  for  substitution  displayed  by  the 
hydrogen  atoms  of  the  benzene-nucleus  after  introduction  of  a 
hydroxyl-group  is  illustrated  by  the  behaviour  of  the  phenols 


§  334]  NITROPHENOLS,  451 

towards  nitric  acid.  To  obtain  nitrobenzene  from  benzene,  it  is 
necessary  to  employ  concentrated  nitric  acid,  whereas  phenol  is 
converted  by  dilute  nitric  acid  at  low  temperatures  into  o-nitro- 
phenol  and  p-nitro  phenol.  The  two  isomerides  can  be  separated  by 
distillation  with  steam,  with  which  only  the  or^o-compound  is 
volatile.  m-Nitrophenol  can  be  prepared  from  w-nitroaniline  by 
the  diazo-reaction.  o-Nitrophenol  has  a  yellow  colour,  and  a 
characteristic  odour.  m-Nitrophenol  and  p-nitrophenol  are 
colourless,  but  resemble  the  or£/io-compound  in  forming  highly 
coloured  phenoxides.  Further  particulars  of  the  nitrophenols 
are  given  in  330  and  331. 

334.  The  most  important  nitrophenol  derivative  is  picric  acid, 
or  U2:4:  6-trinitrophenol, 

N02 


DOH 
3  _  2 


This  substance  has  been  known  for  a  long  time,  and  is  produced  by 
the  action  of  concentrated  nitric  acid  upon  many  substances,  such 
as  silk,  leather,  resins,  aniline,  indigo,  etc.  It  is  prepared  by  dis- 
solving phenol  in  concentrated  sulphuric  acid,  and  carefully  adding 
small  quantities  of  this  solution  to  concentrated  nitric  acid  of  1«4 
specific  gravity.  An  energetic  reaction  ensues,  after  which  the 
mixture  is  warmed  for  some  time  on  a  water-bath:  on  cooling, 
picric  acid  crystallizes  out.  It  cannot  be  further  nitrated  :  in  other 
words,  it  is  the  final  product  of  the  action  of  nitric  acid  upon  phenol. 
This  fact  explains  its  production  by  the  action  of  nitric  acid  upon 
such  heterogeneous  substances. 

When  pure,  solid  picric  acid  has  only  a  very  faint-yellow  colour, 
but  its  aqueous  solution  is  deep  yellow.  It  is  a  strong  acid,  and, 
therefore,  undergoes  considerable  ionization  on  solution  in  water: 
the  yellow  colour  is  characteristic  of  the  anion,  since  the  solution 
of  this  acid  in  petroleum-ether,  in  which  there  is  no  ionization,  is 
colourless;  the  anion,  however,  also  undergoes  tautomerizati  on  ' 
(373)  •  It  ig  slightly  soluble  in  cold  water,  and  is  not  volatile 
with  steam.  It  melts  at  122°;  and  has  an  excessively  bitter 
taste,  which  suggested  its  name  (TTIKPOS,  bitter)  . 

A  consideration  of  the  following  reactions  shows  that  picric 


452  ORGANIC  CHEMISTRY. 


[§334 


acid  is  comparable  with  the  carboxylic  acids.  Phosphorus  penta- 
chlonde  replaces  the  hydroxyl-group  by  chlorine,  with  formation 
f  picryl  chloride  (330).  Silver  picrate  and  methyl  iodide  yield 
methyl  picrate:  it  has  the  properties  of  an  ester,  being  saponified  by 
boiling  with  concentrated  caustic  alkalis,  and  yielding  picramide 
on  treatment  with  ammonia.  These  facts  afford  further  evidence 
of  the  remarkable  increase  in  the  reactivity  of  the  hydroxyl-group, 
due  to  the  presence  of  the  three  nitro-groups. 

Picric  acid  yields  well-defined  crystalline,  explosive  salts,  of  a 
yellow  or  red  colour.  The  potassium  salt  dissolves  with  difficulty 
in  water,  and,  like  the  ammonium  salt,  explodes  by  percussion 
although  the  acid  itself  does  not.  Prolonged  consumption  of 
small  quantities  of  potassium  picrate  imparts  a  yellow  colour  first 
to  the  conjunctiva  of  the  eyes,  and  later  to  the  entire  skin. 

It  yields  molecular  compounds  with  many  aromatic  hydrocar- 
bons; for  example,  with  naphthalene  a  compound  of  the  formula 
CioH8.C6H2(NO2)3-OH.  These  derivatives  crystallize  well,  and 
have  definite  melting-points.  They  are  sometimes  employed' with 
advantage  in  the  separation  of  hydrocarbons,  or  in  their  identi- 
fication. Picric  acid  is  eliminated  from  them  by  the  action  of 
ammonia. 

The  acid  can  be'  detected  by  an  aqueous  solution  of  potassium 
cyanide,  which  yields  a  red  coloration  due  to  the  formation  of 
isopurpuric  acid. 

Picric  acid  is  employed  as  an  explosive,  which  leaves  no  residue 
on  explosion,  and  is  called  '.'  lyddite."  It  was  formerly  used  as  a 
dye,  since  it  imparts  a  yellow  colour  to  wool  and  silk. 

Phenolsulphonic  Acids. 

o-Phenolsulphonic  acid  and  p-phenolsulphonic  acid  are  ob- 
tained by  dissolving  phenol  in  concentrated  sulphuric  acid. 
^-Phenolsulphonic  acid  is  produced  by  fusing  w-benzenedi- 
sulphonic  acid  with  caustic  potash.  The  o-acid  is  characterized 
by  being  easily  converted  into  the  p-compound.  Phenol  sulpho- 
nates  more  readily  than  benzene,  its  solution  in  sulphuric  acid 
being  transformed  into  the  o-sulphonic  acid  and  p-sulphonic  acid 
even  at  ordinary  temperatures. 


§§  335, 3361  NITROSOPHENOL.  453 


Nitrosophenol. 

335.  In  certain  respects  nitrosophenol  reacts  as  though  it  had 
the  constitution  CeEU  <QTT,  although  its  formation  from  quinone 


and  hydroxylamine  points  to  the  constitution  CeH,^  .     It  is 


prepared  by  the  action  of  nitrous  acid  upon  phenol,  or  of  caustic 
potash  upon  nitrosodimethylaniline  (299)  : 


1  = 


=  HN(CH3)  2 


Like  other  oximes,  nitrosophenol,  or  quinone  mono-oxime, 
unites  with  bases.  It  is  a  colourless  compound,  crystallizing  in 
needles  which  soon  turn  brown  on  exposure  to  air.  On  oxidation 
and  reduction,  it  behaves  as  though  it  were  nitrosophenol,  yielding 
nitrophenol  and  aminophenol  respectively. 

336.  Phenol  is  much  more  readily  attacked  by  oxidizing  agents 
than  benzene  (293).  The  polyhydric  phenols  possess  this  property 
to  an  even  greater  extent,  many  of  them  behaving  as  powerful 
reducing  agents  when  dissolved  in  alkalis. 

Dihydric  Phenols. 

OT-T  1 
The  o-compound,  C6H4<nrT  9,  catechol    ("  pyrocatechol  "  or 


"  pyrocatechin  "),  is  a  constituent  of  many  resins,  and  can  be 
prepared  by  fusing  o-phenolsulphonic  acid  with  caustic  potash. 

Catechol  is  crystalline  and  readily  soluble  in  water,  alcohol,  and 
ether.  It  melts  at  104°.  Its  alkaline  solution  is  first  turned  green 
by  atmospheric  oxidation,  and  then  black.  Its  aqueous  solution 
precipitates  metallic  silver  from  silver-nitrate  solution  at  ordinary 
temperatures,  and  gives  a  green  coloration  with  ferric  chloride. 

OPTT    1 
The  monomethyl  ether,  C6H4  <          3  2,  is  called  guaiacol;   it  is 


454 


ORGANIC  CHEMISTRY. 


[§336 


present  in  the  tar  obtained  by  the  dry  distillation  of  beechwood. 
When  heated  with  hydriodic  acid,  guaiacol  yields  catechol  and 
methyl  iodide.  The  dimethyl  ether  of  catechol  is  named  veratrole, 
and  is  characterized  by  .its  agreeable  odour. 

OTT  1 

Resorcinol  ("  resorcin  "),  or  m-dihydroxybenzene,  CGH^QTT  o, 

can     be     obtained     by     fusing     w-phenylenedisulphonic     acid, 

SO  TT  1 

C6H4<gQ3TT  o,  with  potassium  hydroxide,  the  method  for  its  man- 
ufacture. It  jdelds  a  deep-violet  coloration  with  ferric  chloride: 
bromine-water  converts  it  into  tribromoresorcinol.  It  is  a  colour- 
less, crystalline  substance  melting  at  118°,  and  is  readily  soluble 
in  water,  alcohol,  and  ether.  It  quickly  turns  brown,  owing  to 
the  action  of  the  air.  A  delicate  test  for  resorcinol  is  mentioned 
in  347- 

Styphnic  acid,  C6HLTQ\2  W'4*6)  *s  a  ^Pe  °^  a  nitrated  dihy- 

droxybcnzene,  and  is  obtained  by  the  action  of  cold  nitric  acid  upon 
resorcinol,  as  well  as  from  certain  gum-resins  by  the  same  means. 
The  conversion  of  ra-nitrophenol  into  styphnic  acid  by  the  agency  of 
nitric  acid  involves  the  intermediate  formation  of  a  tetranitro-com- 
pound,  in  which  one  of  the  nitro-groups  is  so  reactive  as  to  be 
replaceable  by  hydroxyl  on  treatment  with  water,  with  formation  of 
styphnic  acid: 


OH 
N02/\N02 


OH 


N02 

2:  3:  4:  6-Tetranitrophenol 


H 

N02 

Styphnic  acid 


Quinol  ("  hydroquinone  "),  or  p-dihydroxybenzene,  melts  at 
170°.  Its  chief  characteristic  is  the  loss  on  oxidation  of  two 
hydrogen  atoms  with  formation  of  quinone,  C6H402  (338),  which 
is  readily  reconverted  into  quinol  by  reduction.  The  reducing 
effect  of  quinol  is  employed  in  photography  for  the  development 
of  negatives.  With  ammonia  it  gives  a  red-brown  coloration,  due 
to  the  formation  of  complex  derivatives.  Like  its  isomerides,  it 
is  readily  soluble  in  water. 

The  dihydroxybenzenes  can  be  separated  from  one  another 
by  the  action  of  lead  acetate.  With  this  reagent,  catechol  gives 


§337]  TRIHYDRIC  PHENOLS.  455 

a  white  precipitate,  resorcinol  does  not  yield  a  precipitate,  and 
quinol  gives  a  precipitate  only  in  presence  of  ammonia. 

Trihydric  Phenols. 
337.  Pyrogallol  ("  pyrogallic  acid"), 

OH  1 
2 

\OH3' 

is  obtained  by  heating  gallic  acid  (346),  CO2  being  split  off: 
C6H2(OH)3-COOH-  C6H3(OH)3  +  CO2. 

Gallic  acid  Pyrogallol 

Pyrogallol  forms  crystals  melting  at  132°,  and  is  readily  soluble 
in  water.  It  is  a  strong  reducing  agent  in  alkaline  solution:  for 
example,  it  rapidly  absorbs  the  oxygen  of  the  atmosphere,  with 
formation  of  a  brown  coloration.  For  this  reason  it  is  employed 
in  gas-analysis  to  remove  oxygen  from  mixtures.  It  also  finds 
application  as  a  developer  in  photography,  and  as  an  agent  for 
dyeing  furs. 

xOHl 

Phloroglucinol  (symmetrical  trihydroxybenzene),  CeH^-OH  3, 

is  formed  by  fusing  various  resins  with  potassium  hydroxide.  It  is 
crystalline,  and  gives  a  deep-violet  coloration  with  ferric  chloride. 
A  remarkable  synthesis  of  phloroglucinol  from  diethyl  sodio- 
malonate  was  discovered  by  VON  BAEYER. 

The  mechanism  of  the  reaction  involves  the  preliminary  forma- 
tion of  sodium  ethoxide  under  the  influence  of  heat,  followed  by  the 
combination  of  this  substance  with  part  of  the  diethyl  malonate  to 
form  ethyl  acetate  and  ethyl  carbonate : 

CH,(COOC,H»)»+C2H5OH  =  CH3  •  COOC2H5+C03(C2H5)2. 

Ethyl  acetate         Ethyl  carbonate 

The  ethyl   acetate  condenses   with  diethyl  malonate   to  form  the 
diethyl  ester  of  unsymmetrical  acetonedicarboxylic  acid: 

(COOC2H5)2CH2+C2H5OOC  •  CH3 

=  (COOC2H5)2CH  -  CO  -  CH3+C2H6OH. 

Diethyl  acetonedicarboxylate 


456  ORGANIC  CHEMISTRY.  [§  337 

This  product  then  condenses  with  another  molecule  of  diethyl 
malonate,  with  production  of  diethyl  phloroglucinoldicarboxylate: 

(COOC2H6)2C  Hi  -  CO-CH2|H1  (COOC2H5)2C— CO— CH2 

L+  -  I 

CQ^C2H5CH2  COIOCS]  CO-CH2-CO 

Diethyl  phloroglucinol- 
dicarboxylate 

On  fusing  this  substance  with  potassium  hydroxide,  the  ethyl-car- 
boxyl-groups  ( — COOC2H5)  are  replaced  by  hydrogen,  with  forma- 
tion of  phloroglucinol. 

Phloroglucinol  should  therefore  have  constitution  I. 

CO  H 


H.C       CH2 

OC      CO 
\/ 


CH, 
I.  II. 


In  other  words,  it  is  q/c/ohexane  in  which  three  of  the  methyl- 
ene-groups,  CH2,  have  been  replaced  by  carbonyl,  CO;  it  must, 
therefore,  be  called  triketocyclohexane.  It  has  been  proved  that 
phloroglucinol  does  behave  as  though  it  had  this  constitution:  thus, 
with  three  molecules  of  hydroxylamine  it  yields  a  trioxime.  On  the 
other  hand,  phloroglucinol  has  the  character  of  a  phenol :  for  example, 
it  yields  a  triacetate  with  acetyl  chloride.  It  exists,  therefore,  in 
two  tautomeric  forms — as  a  hexamethylene  derivative,  I.,  and  as 
trihydroxybenzene,  II. 

This  is  a  remarkable  example  of  the  alteration  of  the  positions  of 
the  atoms  (the  hydrogen  of  the  OH-groups)  in  the  molecule,  result- 
ing in  the  conversion  of  a  benzene  derivative  into  a  derivative  of 
hexamethylene. 

This  view  explains  the  interaction  of  phloroglucinol,  and  other 
polyhydric  phenols,  and  a  mixture  of  caustic  potash  and  an  alkyl 
iodide  to  form  derivatives  with  alkyl-groups  attached  to  carbon  and 
not  to  oxygen;  for  the  hydrogen  in  the  methylene-groups  of  the 
tautomeric  form  must  be  replaceable  by  metals  (200). 

The  problem  of  assigning  the  enolic  or  ketonic  formula  to  free 
phloroglucinol  is  settled  by  an  examination  of  the  absorption- 


§  338]  HIGHER  PHENOLS  AND  QUI NONES.  457 

spectrum  of  this  substance  in  alcoholic  solution.  The  ultraviolet 
region  of  this  spectrum  contains  a  band  approximating  closely  in 
position  to  a  similar  band  in  the  spectrum  of  the  trimethyl  ether  of 
phloroglucinol.  Since  this  ether  is  undoubtedly  an  enolic  compound, 
phloroglucinol  itself  must  have  the  enolic  formula;  because  the 
distribution  of  the  bands  in  the  absorption-spectra  of  enolic  com- 
pounds has  been  proved  by  other  researches  to  be  wholly  different 
from  that  of  the  b  ands  in  the  spectra  of  their  ketonic  isomerides. 


Higher  Phenols. 

The  chief  of  the  higher  phenols  is  hexahydroxybenzene,  C6(OH)6. 
Its  potassium  derivative,  potassium  carbonyl,  C6(OK)6,  is  formed 
in  the  preparation  of  potassium,  and  acquires  an  explosive  char- 
acter on  exposure  to  the  air  ("  Inorganic  Chemistry,"  227).  It 
can  be  obtained  by  heating  potassium  in  a  current  of  carbon  monox- 
ide, a  direct  synthesis  of  a  derivative  of  benzene.  Distillation  with 
zinc-dust  converts  hexahydroxybenzene  into  benzene.  It  is  a  white, 
crystalline  substance,  and  undergoes  oxidation  very  readily. 

Quinones. 

338.  The  quinones  are  substances  derived  by  the  elimination 
of  two  hydroxyl-hydrogen  atoms  from  aromatic  dihydroxy-deriva- 
tives: 

C6H4(OH)2-2H  =  C6H4O2. 

Dihydroxybenzene  Quinone 


The  simplest  quinone  is  benzoquinone,  CeH^C^   it  is  also  called 
quinone.     It  is  obtained  by  the  oxidation  of  many  p-derivatives  of 

benzene,  such  as  p-aminophenol  C6H4<QTT2  ,,  sulphanilic  acid, 
C6H4<  ,  and  p-phenolsulphonic  acid, 


also  by  the  oxidation  of  aniline  with  chromic  acid  —  the  ordinary 
method  of  preparation.  It  is  also  formed  in  the  oxidation  of  quinol 
(336),  though  the  latter  is  usually  prepared  by  the  reduction  of 
quinone.  Oxidation  of  quinol  by  ferric  chloride  yields  quin- 
hydrone,  a  compound  in  equimolecular  proportions  of  quinone 
and  quinol,  crystallizing  in  beautiful,  intensely  coloured,  long 
needles. 


458  ORGANIC  CHEMISTRY.  [§  338 

o-Dihydroxybenzene  or  catechol  can  also  be  converted  by  the 
action  of  silver  oxide  into  an  unstable  quinone.  ra-Dihydroxyben- 
zene  or  resorcinol  does  not  yield  a  quinone. 

A  great  number  of  para-quinones  are  known.  Like  benzo- 
quinone,  they  can  be  prepared  by  oxidizing  the  corresponding 
para-compounds. 

The  quinones  are  yellow,  and  have  a  peculiar,  pungent  odour. 
They  volatilize  with  steam  with  partial  decomposition,  and  have 
oxidizing  properties.  The  constitution  of  benzoquinone  is  best 
expressed  by 

CO 

HC        CH 

J   !W 
v 

CO 

Such  a  formula  requires  that  benzoquinone  should  be  a  diketone, 
and  contain  two  double  bonds:  its  properties  show  that  it  fulfils 
both  conditions.  Its  ketonic  character  is  inferred  from  its  yielding 
with  hydroxylamine  first  a  quinone  mono-oxime  (381),  and  then  a 
quinone-dioxime: 

C=NOH  C=NOH 

/\  /\ 

HC        CH  HC        CH 


and 
[C 


HC        CH  HC        CH 

\/.  \/ 

CO  C=NOH 

The  presence  of  double  linkings  is  proved  by  its  power  of  forming 
addition-products:  benzoquinone  in  chloroform  solution  can  take 
up  four  atoms  of  bromine.  According  to  this  constitution,  benzo- 
quinone is  not  a  true  benzene  derivative,  but  the  diketone  of  a 
p-dihydrobenzene : 

CH2 


HC        CH 


CH2 


§  339]  SUBSTITUTION-PRODUCTS  OF  ANILINE.  459 

This  formula  is  supported  by  the  oxidation  of  benzoquinone 
to  maleic  acid,  effected  by  an  alkali-metal  persulphate  in  presence 
of  silver  sulphate  and  sulphuric  acid: 

CO 


+   2C02. 


H 


VI.    SUBSTITUTION-PRODUCTS  OF  ANILINE. 

339.  Aniline  is  attacked  very  energetically  by  chlorine  and 
bromine.  The  direct  introduction  of  these  halogens  must  be 
effected  by  their  slow  addition  to  solution  of  acetoanilide  in 
glacial  acetic  acid,  the  main  products  being  the  para-compounds. 
The  or^o-halogenanilines  and  the  ra^a-halogenanilines  are  pre- 
pared by  reduction  of  the  corresponding  halogen-nitrobenzenes. 
The  production  of  2*4:'.Q-tribromoaniline  is  described  in  296. 
The  basic  character  of  aniline  is  weakened  by  the  introduction 
of  halogens. 

Nitroanilines. 

Nitroanilines,  or  compounds  containing  nitro-groups  and  an 
amino-group,  can  be  obtained  by  the  partial  reduction  of  dinitro- 
compounds  by  means  of  ammonium  sulphide.  Another  method 
for  their  production  consists  in  the  nitration  of  anilines,  though 
if  nitric  acid  is  allowed  to  act  directly  on  this  .base  the  resulting 
products  are  mostly  those  of  oxidation.  If  nitration  is  to  be  car- 
ried out,  the  amino-group  must  be  "  protected  "  against  the  action 
of  this  acid,  either  by  first  converting  the  aniline  into  acetoanilide, 
or  by  causing  the  nitric  acid  to  react  in  presence  of  a  large  quan- 
tity of  sulphuric  acid.  When  the  acetyl-compound  is  employed, 
p-nitroaniline  is  the  chief  product :  with  sulphuric  acid,  m-nitro- 
aniline  and  p-nitroaniline  are  formed  in  almost  equal  ratio,  and  a 
very  small  proportion  of  o-nitroaniline.  The  formation  of  nitro- 
anilines  from  chloronitrobenzenes  and  bromonitrobenzenes  is  men- 
tioned in  330. 


460  ORGANIC  CHEMISTRY.  [§  339 

The  amino-groups  in  o-nitroaniline  and  p-nitroaniline,  but  not 
that  in  ra-nitrouniline,  are  exchanged  for  hydroxyl  by  heating  with 
a  solution  of  potassium  hydroxide,  the  corresponding  potassium 
nitrophenoxide  being  formed.  The  amino-group  in  picramide  or 
2:4::Q-trinitroaniline,  CeH^NC^a-NI^,  is  very  readily  replaced 
by  hydroxyl. 

In  these  substances  there  is  a  weakening  of  the  basic  character, 
o-nitroaniline,  for  example,  yielding  salts  which  are  decomposed 
by  water. 

o-Nitroaniline;  w-nitro aniline,  and  p-nitroaniline,  CeH^^TTr2, 

are  yellow,  crystalline  compounds,  almost  insoluble  in  cold  water, 
but  readily  soluble  in  alcohol.  Their  melting-points  are  respect- 
ively 71°,  114°,  and  147°. 

p-Aminobenzenesulphonic  Acid  or  Sulphanilic  Acid. 

Sulphanilic  acid  is  obtained  by  heating  aniline  with  fum- 
ing sulphuric  acid;  or  by  heating  p-chlorobenzenesulphonic  acid 
at  200°  with  ammonia,  in  presence  of  copper  as  a  catalyst.  Like 
its  isomerides,  it  dissolves  with  difficulty  in  cold  water.  The 
basic  properties  of  aniline  are  greatly  weakened  by  the  intro- 
duction of  the  sulpho-group  into  the  ring,  for  Sulphanilic  acid 
cannot  yield  salts  with  acids,  whereas  the  sulpho-group  reacts 
with  bases,  forming  salts.  The  formula  of  Sulphanilic  acid  is 

SO 
probably  CeH^  <VTTT  >  ;  that  is,  it  is  an  inner  salt.     On  fusion 

with  potassium  hydroxide,  it  does  not  yield  aminophenol,  in  ac- 
cordance with  precedent,  but  aniline.  Oxidation  with  chromic 
acid  converts  it  into  quinone.  On  pouring  a  mixture  of  sodium 
sulphanilate  and  sodium  nitrite  in  aqueous  solution  into  dilute 
sulphuric  acid,  an  inner*  salt  of  benzenediazoniumsulphonic  acid  is 
precipitated,  being  nearly  insoluble  in  water: 


L.      - 


This  compound  is  of  great  importance  in  the  preparation  of  azo- 
dyes,  such  as  helianthine  (341). 


§  339]  AMINOPHENOLS.  461 

'Aminophenols. 

Aminophenols  are  formed  by  the  reduction  of  nitrophenols. 
The  acidic  character  in  these  compounds  is  so  weakened  that  they 
do  not  combine  with  bases:  on  the  other  hand,  they  yield  salts  with 
acids.  In  the  free  state  the  aminophenols  are  colourless  solids, 
crystallizing  in  leaflets,  and  readily  turned  brown  by  atmcspheric 
oxidation  with  formation  of  a  resin.  Their  hydrochlorides  are  more 
stable. 

o-Aminophenol  yields  compounds  by  the  substitution  of  acid- 
residues  in  the  amino-group,  which  at  once  lose  water,  forming 
anhydro-bases: 

CHa 

|NH2_>  (/N|1*|H  ' 

'OH      \/O[H 

Acetyl-derivative  Ethenylaminophenol, 

Anhydro-base 

On  treatment  with  acids,  aminophenol  and  acetic  acid  are  regen- 
erated. 

p-Aminophenol  is  obtained  by  the  electro-reduction  of  nitro- 
benzene in  acid  solution  (303) . 

The  alkaline  solution  of  p-aminophenol  rapidly  acquires  a  dark 
colour,  unless  sodium  sulphite  is  present.  The  trade-name  of  this 
solution  is  "rodinal."  It  finds  application  as  a  photographic 
developer. 

LUMIERE  has  discovered  certain  general  conditions  which  aro- 
matic compounds  must  fulfil  to  be  available  as  photographic  devel- 
opers. They  must  either  contain  some  hydroxyl-groups  or  amino- 
groups,  or  at  least  one  of  each  class.  In  order  that  the  developing 
action  may  not  be  interfered  with  when  substituents  are  present  in 
the  amino-group  and  in  the  hydroxyl-group,  not  less  than  two  such 
unsubstituted  groups  must  be  present  in  the  molecule. 

A  derivative  of  p-aminophenol  used  in  medicine  is  "phenacetin  " 

or  acetylphenetidine,  C6H4<VH2  £  „  n,  the  acetamino-derivative  of 


phenetole,  C6H5-OC2H5. 

When  aniline  hydroarsenate,  C6H5-  XH^HsAsO^  is  heated,  a  mole- 
cule of  water  is  eliminated,  with  formation  of  p-aminophe.nylarsinic 
acid,  NH2 -CeH^AsOCOH)^  The  presence  of  a  free  amino-group 


462  ORGANIC  CHEMISTRY.  [§339 

is  proved  by  the  possibility  of  diazotizing  the  compound;  iodine 
converts  it  into  p-iodoaniline,  with  elimination  of  the  arsenic-acid 
residue.  The  formation  of  p-aminophenjdarsinic  acid  is  analogous 
to  that  of  sulphanilic  acid  by  heating  aniline  hydrogen  sulphate: 

C6H5.NH2,H2S04-H20=NH2.C6H4.S03H. 

Aniline  hydrogen  Sulphanilic  acid 

sulphate 

Sodium  p-aminophenylarsinate  or  "  atoxyl,"  and  sodium  p-acetyl- 
aminophenylarsinate  or  "  arsacetin," 

CH3  -  CO  -  NH  •  C6H4  •  AsO  < 


are  valuable  remedies  for  the  treatment  of  trypanosomiasis  or  sleeping 
sickness. 

When  phenol  is  heated  with  arsenic  acid,  it  yields  the  analogous 
p-hydroxyphenylarsinic  acid,  HO-C6H4-AsO(OH)2,  converted  by 
careful  nitration  into  3-nitro-4:-hydroxyphenylarsinic  acid, 


HO/~~\AsO(OH)2. 


O2N 

Reduction    transforms    this    product    into    the    corresponding 
diaminodihydroxyarsenobenzene, 


H2N 

The  dihydrochloride  of  this  substance  is  the  "  salvarsan  " 
discovered  by  EHRLICH  and  HATA,  and  has  been  employed  with 
good  results  in  the  treatment  of  diseases  of  protozoal  origin.  It 
is  a  crystalline  powder,  readily  soluble  in  hot  water,  but  the 
solution  decomposes  rapidly. 

Polyamino-compounds  are  obtained  by  the  reduction  of  poly- 

nitro-derivatives.     m-Phenylenediamine,  C&H.4  <^pr2  o,  is  formed 

from  benzene  by  nitration  and  subsequent  reduction. 

p-Phenylenediamine  can  be  prepared  by  the  reduction  of  amino- 


§  3391  POLYAMINO-COMPOUNDS.  463 

azobenzene  (309)  with  tin  and  hydrochloric  acid,  aniline  being  also 
formed  : 


2HI2H 

Triaminobenzenes  are  prepared  similarly  (341). 

When  heated  with  aqueous  ammonia  at  180°-200°,  in  presence 
of  cupric  sulphate  as  a  catalyst,  p-dichlorobenzene  and  p-chloro- 
aiiiline  are  converted  into  the  corresponding  diamine. 

Most  of  the  polyaminobenzenes  are  crystalline  solids,  and 
distil  without  decomposition.  They  dissolve  readily  in  warm 
water. 

The  three  diaminobenzenes  are  distinguished  by  the  following 
series  of  reactions.  The  o-diamines  react  readily  with  l:2-dike- 
tones,  yielding  quinoxalines: 

N=C—  R 

+  2H20. 
N=C—  R' 

m-Phenylenediamine  in  aqueous  solution  gives  an  intense  brown 
coloration  with  nitrous  acid,  even  when  the  acid  solution  is  very 
dilute  (341).  p-Phenylenediamine  is  converted  by  oxidation  into 
benzoquinone. 

Like  the  polyhydric  phenols,  the  polyamino-compounds  are 
very  readily  oxidized.  They  are  colourless,  but  many  of  them  are 
turned  brown  by  oxidation  in  the  air. 

Quinonedi-imide,  HN:C6H4:NH,  a  compound  derived  from 
p-phenylenediamine,  has  the  same  relationship  to  this  amine  as 
benzoquinone  to  quinol.  Aniline-black  is  a  complex  derivative  of 
this  substance,  and  is  formed  by  the  oxidation  of  aniline.  It  is  a 
condensation-product  of  eight  molecules  of  aniline,  and  is  con- 
sidered to  have  the  constitutional  formula 


N:C«H4:NH, 

indicating  union  of  the  eight  aniline-residues  by  nitrogen  and  not 
by  carbon.     One  of  the  arguments  in  favour  of  this  formula  is  the 


464  ORGANIC  CHEMISTRY.  [§340 

almost  quantitative  conversion  of  aniline-black  by  further  oxidation 
into  benzoquinone,  also  a  proof  that  each  of  the  eight  aniline-residues 
is  linked  at  the  para-position. 

Azo-dyes. 

340.  The  azo-derivatives  of  the  polyamino-compounds  are 
known  as  azo-dyes.  They  are  of  great  technical  importance,  being 
extensively  employed  in  dyeing  wool,  silk,  and  cotton.  They  are 
azobenzenes  in  which  hydrogen  atoms  have  been  replaced  by 
amino-groups.  They  are  not  the  only  dyes:  derivatives  of  azo- 
benzene  with  hydrogen  replaced  by  hydroxyl  or  by  the  sulpho- 
group  can  likewise  be  employed  in  dyeing.  Some  of  these  com- 
pounds will  also  be  described. 

It  is  necessary  first  to  state  certain  facts  regarding  dyes  in 
general.  It  has  been  proved  by  experiment  that  not  every  colour- 
ing-matter can  dye  the  substances  named  above;  that  is,  colour 
them  so  that  the  dye  cannot  subsequently  be  removed  by  rubbing, 
or  washing  with  water  or  soap.  It  is  necessary,  therefore,  to  draw 
a  distinction  between  coloured  substances,  or  chromogens,  and 
dyes:  for  example,  azobenzene  has  a  deep  yellowish-red  colour, 
but  it  is  not  a  dye.  The  introduction  of  an  amino-group,  however, 
converts  it  into  a  dye,  aminoazobenzene.  WITT  has  propounded 
the  theory  that  the  colouring-power  of  a  compound  depends  upon 
two  factors.  The  first  of  these  is  the  presence  of  certain  groups, 
which  he  calls  chromophoru-groups,  among  them  being  the  azo- 
group,  — N=N — ,  the  nitro-group,  the  nitroso-group,  the  double 
carbon  linking  — C— C — ,  the  carbon  ring  present  in  benzo- 
quinone or  quinonoid-group  =S  /=,  and  other  groups. 

Substances  containing  a  chromophore-group,  along  with  an 
auxochrome'ic-group,  such  as  NHo,  OH,  SOsH,  or  in  general  any 
group  which  imparts  to  them  an  acidic  or  basic  character,  are 
dyes:  an  example  is  aminoazobenzene.  Another  example  is 
nitrobenzene,  which  has  a  pale-yellow  colour,  and  contains  the 
ehromophore  nitro-group,  but  is  a  chromogen,  not  a  dye :  on  the 
other  hand,  p-nitroaniline  and  p-nitrophenol  are  dyes. 

BALY  has  shown  that  many  colourless  compounds,  especially 
those  with  double  carbon  linkings,  are  characterized  by  absorption- 
bands  in  the  ultraviolet  spectrum.  The  introduction  of  auxo- 


§  341]  AZO-DYES.  465 

chrome'ic  groups  into  such  substances  displaces  these  bands  to  the 
visible  part  of  the  spectrum;  in  other  words,  transforms  these 
compounds  into  dyes. 

It  is  often  sufficient  to  immerse  the  silk,  wool,  or  cotton  to 
be  dyed  in  a  solution  of  the  dye.  Although  primarily  dissolved,  the 
dye  cannot  be  removed  by  washing  the  fabric  after  dyeing.  The 
dye  must,  therefore,  have  undergone  a  change.  It  is  assumed  that 
it  unites  with  the  constituents  of  the  animal  or  vegetable  fibres  to 
form  a  compound,  a  kind  of  salt,  since  dyes  always  have  a  basic  or 
acidic  character.  A  proof  of  this  is  given  for  rosaniline  (374). 

The  fabric  does  not  always  take  up  the  dye  when  -immersed  in 
its  solution.  It  has  been  repeatedly  observed  that  dyes  which 
become  directly  fixed  on  animal  fabrics,  such  as  silk  and  wool,  do  not 
dye  vegetable  fabrics,  like  cotton,  unless  the  material  to  be  dyed  has 
undergone  a  special  process,  called  "mordanting":  that  is,  a  sub- 
stance must  be  deposited  in  the  fabric  to  "fix"  the  dye,  since  it  will 
not  unite  with  the  fibres  themselves.  Such  substances  are  called 
"mordants":  they  are  usually  salts  of  weak  bases  or  acids.  Such 
are  aluminium  acetate;  ferric  salts;  compounds  of  tin,  such  as 
"pink  salt,"  SnCl4,2XH4Cl.  The  woven  material  is  thoroughly 
soaked  in  a  solution  of  one  of  these  salts,  and  then  spread  out  and 
exposed  to  the  action  of  steam  at  a  suitable  temperature.  The  salt 
undergoes  hydrolytic  dissociation,  and  the  base  or  acid,  for  example 
aluminium  hydroxide  or  stannic  acid,  is  deposited  in  a  fine  state  of 
division  in  the  fabric.  The  dye  unites  with  this  base  or  acid,  forming 
an  insoluble,  coloured  compound  which  is  not  removed  by  washing. 

Direct  dyes  are  those  capable  of  colouring  the  fabric  without 
previous  mordanting. 

341.  Azo-dyes  are  obtained  by  treating  diazonium  chlorides 
with  aromatic  amines  or  with  phenols: 

C6H5«X2[Cl+Hl<^"'^>X(CH3)2=C6H5»N:iN'C6H4'N(CH3)24-HCl;, 

Diazonium  chloride        Dimethylaniline  Dimethylaminoazobenzene 

CGH5 •  N2 [Cl  +  H]/"  "NOH - C6H5 •  X : N •  C6H4 •  OH  +  HCL 

N f  Hydroxyazobenzene 

Basic  and  acidic  dyes  respectively  are  produced.  It  is  mentioned 
in  309  that  the  combination  of  a  diazonium  chloride  and  an  aro- 
matic amine  sometimes  yields  the  diazoamino-compound  as  an 


466  ORGANIC  CHEMISTRY.  [§  341 

intermediate  product,  which  can  be  converted  into  the  aminoazo- 
derivative  by  warming  with  the  amine  hydrochloride.  In  this 
formation  of  aminoazo-compounds  and  hydroxyazo-compounds, 
the  para-H-atom  always  reacts  with  the  diazonium  chloride :  when 
this  atom  is  replaced  by  a  substituent,  the  formation  of  dye  either 
does  not  take  place,  or  is  very  incomplete. 

In  preparing  hydroxyazo-dyes,  the  solution  of  the  diazonium 
chloride  is  cooled  with  ice,  and  is  slowly  added  to  the  alkaline  solu- 
tion of  the  phenol  or  its  sul phonic  acid.  The  reaction-mixture  is 
kept  slightly  alkaline,  since  otherwise  the  hydrochloric  acid  liberated 
would  hinder  the  formation  of  the  dye.  After  the  solutions  have 
been  mixed,  the  dye  is  "  salted  out  "  by  the  addition  of  common 
salt,  which  precipitates  it  in  flocculent  masses.  It  is  freed  from 
water  by  means  of  filter-presses,  and  packed  either  as  a  powder  or  a 
paste. 

Aminoazo-dyes  are  prepared  by  mixing  the  aqueous  solution  of 
the  diazonium  chloride  with  that  of  the  aromatic  amine  salt,  the 
colouring-matter  being  subsequently  salted  out.  It  is  sometimes 
necessary  to  employ  an  alcoholic  solution. 

The  simplest  azo-dyes  are  yellow.  The  introduction  of  alkyl- 
groups  or  phenyl-groups,  and,  in  general,  increase  of  molecular 
weight,  change  their  colour  through  orange  and  red  to  violet  and  blue. 
They  .are  crystalline,  and  most  of  them  are  insoluble  in  water  and 
soluble  in  alcohol.  Instead  of  the  azo-dyes  themselves,  it  is  often 
better  to  employ  their  sulphonic  acids,  obtainable  from 'them  by  the 
usual  method — treatment  with  concentrated  sulphuric  acid. 


Aniline-yellow  is  a  salt  of  aminoazobenzene  :  it  is  seldom  use.l 
now,  its  place  having  been  taken  by  other  yellow  dyes. 

-VTTT 

Chrysoldine  or  diaminoazobenzene,  C6rl5«N:N'C6H3  <Ajr2,  is 


obtained  from  benzenediazonium  chloride  and  w-phenylenedia- 
mine.  It  yields  a  hydrochloride,  crystallizing  in  needles  of  a 
reddish  colour  and  fairly  soluble  in  water:  this  salt  dyes  wool 
and  silk  directly,  and  cotton  which  has  been  mordanted. 

Bismarck-brown  or  vesuvine  is  formed  by  addition  of  nitrous 
acid  to  an  aqueous  solution  of  m-phenylenedi  amine.  It  is  a 
mixture  of  various  dyes,  among  them  triaminoazobenzene,  manu- 


I  341]  AZO-DYES.  467 

factured  by  diazotizing  one  of  the  NH2-groups  in  w-phenylene- 
diamine,  and  treating  the  product  thus  obtained  with  a  second 
molecule  of  this  base  : 


H2N  H2X  H2X  H2N 

Triaminoazobenzene 

Bismarck-brown  consists  mainly  of  more  complex  derivatives, 
formed  by  diazotization  of  both  the  amino-groups  of  w-phenyl- 
enediamine  and  union  of  the  products  with  two  molecules  of  this 
base. 

Even  a  very  dilute  solution  of  nitrous  acid  gives  a  brown  colora- 
tion with  w-phenylenediamine,  due  to  the  formation  of  Bismarck- 
brown  or  related  substances.  This  reaction  furnishes  a  very  delicate 
test  for  nitrous  acid,  and  is  employed  in  water-analysis.  . 

Helianthine,  or  dimethylaminoazobenzenesulphonic  acid,  is  pre- 
pared by  the  interaction  of  p-sulphobenzenediazonium  chloride 
and  dimethylaniline  hydrochloride  in  aqueous  solution  : 


=HC1  +  HO3S.C6H4-N:N.C6H4-N(CH3)2. 

Helianthine 

It  is  not  often  used  as  a  dye,  but  its  sodium  salt,  which  has  a 
yellow  colour,  and  is  turned  red  by  acids,  is  employed  as  an, 
indicator  in  volumetric  analysis  under  the  name  methyl-orange. 
Resor  tin-  yellow  or  dihydroxyazobenzenesulphonic  acid, 

H03S  •  C6H4  -  N  :  N  •  C6H3  < 


is  obtained  from  resorcinol  (336)  and  p-sulphobenzenediazonium, 
chloride. 

The  azo-dyes  are  converted  into  amino-compounds  by  energetic 
reduction  with  tin  and  hydrochloric  acid.  Thus,  aminoazobenzene 
yields  aniline  and  p-phenylenediamine  : 


C6H5  •  N—  N  •  C6H4  •  NH2  -»  C6H5  •  NH2  +  C6H4  < 


468  ORGANIC  CHEMISTRY.  [§  342 

This  decomposition  on  reduction  affords  a  means  of  determining 
the  constitution  of  these  dyes,  and  indicates  the  methods  by  which 
they  are  obtained.  For  example,  if  reduction  of  a  dye  with 
tin  and  hydrochloric  acid  yields  a  mixture  of  equimolecular 
amounts  of  diaminobenzene  and  triaminobenzene,  it  follows  that 
the  constitution  of  this  compound  is 

NH2  •  C6H4— N :  j  N— C6H3  <^. 

This  decomposition  also  indicates  that  the  dye  can  be  obtained  by 
diazotizing  a  molecule  of  diaminobenzene,  and  treating  the  product 
with  a  second  molecule  of  diaminobenzene,  in  accordance  with  the 
equation  on  the  previous  page. 


VH.   SUBSTITUTED  BENZOIC  ACIDS;  POL YB ASIC  ACIDS  AND  THEIR 

DERIVATIVES. 

Halogenbenzoic  Acids. 

342.  Direct  chlorination,  with  ferric  chloride  as  catalyst,  con- 
verts benzoic  acid  into  a  complex  mixture  of  acids.  The  only 
monochloro-constituent  of  the  product  is  m-chlorobenzolc  acid,  it 
being  associated  with  polychloro-acids  very  difficult  to  separate. 
m-Chlorobenzoi'c  acid,  can  also  be  obtained  from  the  corresponding 
amino-derivative  by  the  diazotization-method,  a  reaction  well 
adapted  to  the  preparation  of  the  halogenbenzo'ic  acids.  The 
interaction  of  phosphorus  pentachloride  with  the  hydroxybenzoi'c 
acids  proceeds  less  smoothly.  p-Chlorobenzo'ic  acid  and  p-bromo- 
benzo'ic  acid  are  usually  prepared  by  oxidation  of  the  corre- 
sponding halogentoluenes. 

As  would  be  expected,  the  acidic  character  of  benzoic  acid  is 
strengthened  by  the  introduction  of  halogen.  The  dissociation- 
constant  I04k  of  the  halogenbenzo'ic  acids  is  greater  than  that  of 
benzoic  acid  itself.  For  benzoic  acid  W4k  is  0-6;  for  o-chloroben- 
zoic  acid  13 '2;  for  m-chlorobenzoic  acid  1-55;  for  p-chlofobenzoic 
acid  0-93.  These  values  prove  that  the  chlorine  atom  in  the  ortho- 
position  exercises  the  greatest  influence  and  that  in  the  para- 
position  the  least,  while  for  the  m-compound  I04k  is  intermediate 
in  value. 


§343]       NITROBENZOIC  AND  SULPHO'BENZOIC  ACIDS.          469 

Nitrobenzoiic  Acids. 

m-Nitrobenzolc  acid  is  the  principal  product  obtained  by 
nitrating  benzoic  acid;  about  20  per  cent,  o-nitrobenzoic  acid  and 
a  very  small  proportion  of  p-nitrobenzoic  acid  are  simultaneously 
formed.  The  or£/io-compound  is  best  obtained  by  the  oxidation 
of  o-nitrotoluene,  and  is  characterized  by  an  intensely  sweet 
taste. 

The  introduction  of  the  nitro-group  causes  a  large  increase  in 
the  value  of  the  dissociation-constant  104&,  which  for  benzoic 
acid  itself  is  0*6,  for  o-nitrobenzoic  acid  61  •  6,  for  the  w-acid  3-45, 
and  for  the  p-acid  3-96.  The  melting-points  of  these  acids  are 
respectively  148°,  141°,  and  241.° 

Sulphobenzoic  Acids. 
343.  o-Benzo'ic  sulphinide, 

CeH^  <  QQ  >  NH, 

the  imino-derivative  of  o-sulphobenzo'ic  acid,  is  known  as  "  sac- 
charin." It  is  about  five  hundred  times  as  sweet  as  sugar,  and  on 
this  account  is  sometimes  employed  as  a  substitute  for  it.  It 
has  no  dietetic  value,  being  eliminated  unchanged  from  the  body. 
Direct  sulphonation  of  benzoic  acid  yields  m-sulphobenzoic  acid 
almost  exclusively,  so  that  saccharin  cannot  be  prepared  by  this 
means.  It  is  obtained  from  toluene,  which,  on  treatment  with 
chlorosulphonic  acid,  S02(OH)C1,  yields  a  mixture  of  p-toluene- 
sulphonyl  chloride  and  o-toluenesulphonyl  chloride,  the  former  being 
the  chief  product.  The  o-chloride  is  converted  into  its  sulphon- 
amide,  the  methyl-group  of  which  is  then  transformed  into  carboxyl 
by  oxidation  with  potassium  permanganate.  On  heating,  this 
oxidation-product  loses  one  molecule  of  water  very  readily,  form- 
ing saccharin : 

^Hs  — >  CgH^  <C/-(Tj      o — *  Q>H4  <Cr»Tj  — > 

UH3      Z  v^.n.3 

Toluene          o-Toluenesulphonyl  chloride        o-Sulphonamide 


o-Sulphonamide  of  Saccharin 

benzoic  acid 


470  ORGANIC  CHEMISTRY.  [§  344 

Saccharin  is  a  white,  crystalline  powder,  soluble  with  difficulty 
in  cold  water,  and  readily  soluble  in  alcohol  and  ether.  It  takes 
up  one  molecule  of  water,  yielding  the  sulphamide  of  o-sulpho- 
benzoic  acid,  which  does  not  possess  a  sweet  taste. 

REMSEN  found  that  the  "saccharin"  of  commerce  is  a  mixture  of  o- 
benzoic  sulphinide;  p-sulphaminobenzoic  acid,  COOEU-CeHi-SC^NEk; 
and  potassium  hydrogen  o-sulphobenzoate,  COOH-C6H4'S02OK,  con- 
taining less  than  fifty  per  cent,  of  the  sulphinide.  The  melting-point 
of  the  pure  sulphinide  is  220°. 

Monohydroxy-acids. 

344.  The    most    important    of    the    monohydroxy-acids    is 

OTT        1 
o-hydroxybenzo'ic    acid,    or    salicylic    acid,    C6H4  <  QQQJJ  o-     -^ 

derives  its  name  from  salicin,  a  giucoside  in  the  bark  and  leaves  of 
the  willow  (salix).  On  hydrolysis,  this  substance  yields  saligenin 
and  dextrose: 

Ci3H1807+H2O  =  C7H8O2+C6H12O6. 

Saliciu  Saligenin         Dextrose 

Saligenin  is  the  alcohol  corresponding  to  salicylic  acid,  into  which 
it  is  converted  by  oxidation: 

CeH4  <  CH2OH  ~>  CeH4  <  GOGH' 

Saligenin  Salicylic  acid 

Salicylic  acid  is  present  as  methyl  ester  in  oil  of  wintergreen 
(Gaultheria  procumbens),  from  which  the  acid  is  sometimes  obtained 
for  pharmaceutical  use.  A  good  yield  of  the  acid  is  obtained  by 
fusing  o-cresol  with  caustic  alkali  and  lead  peroxide  as  an  oxidizer: 

/CH3  /COOH 

C6H4<  -»     C6H4< 

XOH  XOH 

Salicylic .  acid  is  manufactured  by  a  process  discovered  by 
KOLBE  and  improved  by  SCHMIDT,  in  which  sodium  phenoxide  is 
heated  with  carbon  dioxide  in  an  autoclave  at  130°. 


344]  MONOHYDROXY-ACIDS.  471 

At  the  ordinary  temperature  at  a  pressure  of  about  l£  atmos- 
pheres, sodium  phenoxide  and  carbon  dioxide  react  to  form  sodium 
phenylcarbo  nate : 


C6H5-0-Na  +  CO2  =  C6H5-0-COONa. 

This  compound  is  to  be  regarded  as  an  intermediate  product  in  the 
synthesis  of  salicyclic  acid.  Its  conversion  into  this  substance  is 
represented  by  the  scheme 

>.COONa  X)H 

4\COONa' 

Salicylic  acid  is  a  white,  crystalline  powder,  which  dissolves 
with  difficulty  in  cold  water,  and  melts  at  159°.  When  carefully 
heated,  it  sublimes,  but  on  rapid  heating  decomposes  into  phenol 
and  carbon  dioxide.  With  bromine-water  it  yields  a  precipitate 
of  the  formula  C6H2Br3.OBr.  It  gives  a  violet  coloration  with 
ferric  chloride,  both  in  aqueous  and  in  alcoholic  solution,  whereas 
phenol  dissolved  in  alcohol  does  not.  When  boiled  with  calcium 
chloride  and  ammonia,  a  solution  of  salicylic  acid  precipitates  basic 

calcium  salicylate,  C6H4<C   ( }   ^Ca:  this  reaction  affords  a  means  of 


separating  salicylic  acid   from  its  isomerides,  which  do  not  give 
this  reaction. 

Salicylic  acid  is  a  powerful  antiseptic,  and  is  employed  as  a 
preservative  for  foods  and  such  beverages  as  beer.  It  is  not,  how- 
ever, completely  innocuous.  Sodium  salicylate  and  the  acetyl- 

/O.CO-CHs 

derivative,    "  aspirin/'     C6H4/  ,    are     employed     in 

medicine.  XCOOH 

When  the  acid  is  heated  to  220°,  it  loses  carbon  dioxide  and 
water,  with  formation  of  phenyl  salicylate: 


This  compound  is  employed  as  an  antiseptic  under  the  name 
"salol."  By  heating  to  300°,  its  sodium  derivative  is  converted 
into  sodium  phenylsalicylate: 

ONa  ^rp    /OC6H5 

COOC6H5  ~  °6H4<  COONa' 


472 


ORGANIC   CHEMISTRY. 


[§  345 


345.  A  large  number  of  vegetable  dyes  related  to  salicylic  acid 
is  known.  They  are  classified  in  two  divisions,  the  xanthone-group 
and  the  flavone-group,  and  have  been  investigated  mainly  by  VON 
KOSTANECKI.  Distillation  of  salicylic  acid  with  acetic  anhydride 

OP  TT 


yields  first  the  phenyl  ether  of  salicylic  acid, 
converted  by  elimination  of  water  into  xanthone, 

0 


,  further 


^\/\^ 

CO 

Euxanthone  or  Indian  yellow  is  a  1  •  2'-dihydroxyxanthone. 
Flavone, 


is  obtained  by  condensation  of  the  ester  of  the  ethyl  ether  of  salicylic 
acid  with  acetophenone : 


/-><    TT        .,  WV^2J--«-.')  /~1    TT         -,WVV2rT5 

CQ[OC2H5+HiCH2-CO»C6H5~  CO-CH2-CO-C6H5 

+C2H6OH 

On  heating  this  condensation-product  with  hydrogen  iodide,  one 
of  the  carbonyl-groups  is  reduced  to  CHOH.  Water  and  alcohol 
are  then  eliminated,  with  formation  of  flavone: 

,0 


C6H4<C0.CH  . 

The     flavone-group    includes    chrysin    or    l*3-dihydroxyflavone, 
the  yellow  dye  of  poplar  buds;  luteolin  or  1  '^•^"•^.'-tetrahydroxy- 
flavone,  the  dye  of  weld  and  dyers'  broom;  morin,  or  1 :3 :2'  i^'-tetra- 
hydroxyflavone,  the  dye  of  Morus  tinctoria;  and  other  products. 
m-Hydroxybenzoic  acid  and  p-hydr ox y benzole  acid  yield  no  colora- 
tion with  ferric  chloride.     Their  basic  barium  salts  are  insoluble. 

Dihydroxy-acids. 

Among  the  dihydroxy-acids  is  proiocatechuic  acid, 

/COOH  1 


C6H3f-OH 


\ 


OH 


§346]         DIHYDROXY-ACIDS  AND  TRIHYDROXY-ACIDS.          473 

It  is  obtained  from  many  resins  by  fusion  with  potash,  and  syn- 
thetically by  heating  catechol  with  ammonium  carbonate,  the  latter 
method  being  a  striking  example  of  the  readiness  with  which  the 
carboxyl-group  can  sometimes  be  introduced  into  the  ring.  It  is 
freely  soluble  in  water.  It  reduces  an  ammoniacal  silver  solution. 
but  not  an  alkaline  copper  solution.  It  gives  a  characteristic 
reaction  with  ferric  chloride,  yielding  a  green  colour,  which  changes 
to  blue  and  finally  to  red  on  addition  of  a  very  dilute  solution  of 
sodium  carbonate. 

Trihydroxy-acids. 
346.  The  best-known  trihydroxy-acid  is  gallic  acid, 

/COOH  1 
3 


\OH       5 

It  is  a  constituent  of  gall-nuts,  tea,  and  "divi-divi,"  a  material 
used  in  tanning.  It  is  usually  prepared  by  boiling  tannin  with 
dilute  acids.  It  crystallizes  in  fine  needles,  readily  soluble  in  hot 
water.  It  is  mentioned  in  337  that,  on  heating,  the  acid  loses  CO2, 
forming  pyrogallol.  Gallic  acid  reduces  the  salts  of  gold  and  silver, 
and  gives  a  bluish-black  precipitate  with  ferric  chloride.  In  alka- 
line solution  it  is  turned  brown  in  the  air  by  oxidation,  like  pyro- 
gallol. 

Gallic  acid  is  employed  in  the  manufacture  of  blue-black  ink. 
For  this  purpose  its  aqueous  solution  is  mixed  with  a  solution  of 
ferrous  sulphate  containing  a  trace  of  free  sulphuric  acid.  Without 
the  acid,  the  ferrous  sulphate  would  quickly  oxidize  in  the  air,  giving 
a  thick,  black  precipitate  with  the  gallic  acid:  this  oxidation  is  re- 
tarded in  a  remarkable  manner  by  the  addition  of  a  very  small  quan- 
tity of  sulphuric  acid.  As  soon  as  the  solution  is  brought  into  con- 
tact with  paper,  the  free  acid  is  neutralized  by  the  alumina  always 
present  in  the  latter,  and,  as  oxidation  is  no  longer  prevented,  the 
writing  in  drying  turns  deep  black.  As  the  mixture  of  the  solutions 
of  ferrous  sulphate  and  gallic  acid  has  only  a  faint-brown  colour, 
which  would  make  the  fresh  writing  almost  invisible,  indigo-carmine 
is  added  to  the  mixture.  This  imparts  to  the  ink  coming  from  the 
pen  a  dark-blue  colour,  which  changes  by  the  process  described  to  a 
deep  black. 


474  ORGANIC   CHEMISTRY.  [§  346 

The  tannins,  or  tannic  acids,  are  very  closely  related  to  gal- 
lic acid,  and  are  widely  distributed  in  the  vegetable  kingdom.  The 
tannins  are  compounds  which  are  soluble  in  water,  have  a  bitter, 
astringent  taste,  yield  a  dark-blue  or  green  precipitate  with  ferric 
salts,  convert  substances  containing  gelatin — such  as  animal  hides 
— into  leather,  and  precipitate  proteins  from  their  solutions. 

A  distinction  is  drawn  between  the  different  kinds  of  tanning- 
substances,  which  have  properties  analogous  to  those  of  tannin, 
but  differ  from  it  in  composition.  They  are  named  after  the  plants 
in  which  they  are  found:  kino-tannin,  catechu-tannin,  moringa- 
tannin,  coffee-tannin,  oak-tannin,  quinine-tannin,  and  others  are 
known. 

The  most  typical  tanning-material  is  tannin  or  tannic  acid,  con- 
tained in  oak-bark.  It  is  converted  by  hydrolysis  with  dilute 
sulphuric  acid  into  gallic  acid  and  dextrose.  This  decomposi- 
tion has  induced  EMIL  FISCHER  to  regard  tannin  as  probably 
having  the  constitution  of  a  pentadigalloylglucose, 

C6H706[C6H2(OH)3-CO.O.C6H2(OH)2CO]5     or      C76R52O46, 

a  view  in  good  accordance  with  all  previous  observations  of 
its  optical  activity,  molecular  weight,  and  slight  acidity.  EMIL 
FISCHER  has  succeeded  in  synthesizing  from  dextrose  and  gallic 
acid  an  artificial  product,  and  although  it  is  not  identical  with 
tannin,  it  resembles  it  closely  in  optical  activity,  the  power  of 
precipitating  gelatin  and  alkaloids,  the  formation  of  a  colora- 
tion with  iron  salts,  slightly  acidic  character,  solubilities,  and 
taste. 

The  best  source  of  tannin  is  furnished  by  gall-nuts — path- 
ological excrescences  on  the  leaves  and  branches  of  the  oak, 
caused  by  an  insect.  Turkish  gall-nuts  are  especially  rich  in 
tannin,  yielding  as  much  as  65  per  cent. 

Tannin  imparts  its  characteristic  bitter  taste  to  many  beverages 
: — to  tea  which  has  been  too  long  infused,  for  instance.  The  addition 
of  milk  removes  this  bitter  taste,  because  the  tannin  forms  an  insol- 
uble compound  with  the  proteins  present  in  the  milk. 

Tannin  is  a  white  (sometimes  yellowish),  amorphous  powder, 
readily  soluble  in  water,  only  slightly  in  alcohol,  and  insoluble  in 


§  346  AMINOBENZOIC  ACIDS.  475 

ether.  It  forms  salts  with  two  equivalents  of  the  metals,  and 
precipitates  many  alkaloids,  such  as  strychnine  and  quinine,  from 
their  aqueous  solutions  (407). 

The  tannins  find  application  in  medicine  and  in  the  tanning  of 
hides. 

In  making  leather,  the  hide  is  saturated  with  the  tannin,  because 
without  this  treatment  it  cannot  be  employed  in  the  manufacture 
of  shoes  and  other  articles,  since  it  soon  dries  to  a  hard,  horn-like  , 
substance,  or  in  the  moist  condition  becomes  rotten.     When  satu- 
rated with  tannin  it  remains  pliant,  and  does  not  decompose. 

The  skin  of  an  animal  consists  of  three  layers,  the  epidermis,  the 
cuticle,  and  the  fatty  layer.  The  cuticle  being  the  part  made  into 
leather,  the  two  other  layers  are  removed  by  suspending  the  hides  in 
running  water,  when  the  epidermis  and  fatty  layer  begin  to  decom- 
pose, and  are  removed  by  means  of  a  blunt  knife.  Alternate  hori- 
zontal layers  of  the  hides  thus  prepared  and  oak-bark  or  some  other 
material  containing  tannin  are  placed  in  large  troughs  or  vats, 
which  are  then  filled  with  water.  At  the  end  of  six  or  eight  weeks 
the  hides  are  taken  out  and  placed  in  a  second  vat  containing  fresh 
bark  of  stronger  quality.  This  is  continued  with  increasingly  concen- 
trated tannin  solutions  until  the  hides  are  perfectly  tanned,  the  proc- 
ess lasting  as  long  as  two  or  three  years,  according  to  the  thickness 
of  the  hide.  Whether  a  hide  is  thoroughly  saturated  or  tanned  can 
be  judged  from  the  appearance  of  its  cross-section,  or  by  treatment 
with  dilute  acetic  acid:  if  this  treatment  makes  it  swell  up  internally, 
it  shows  that  the  conversion  into  leather  is  incomplete. 

During  the  process  of  tanning,  oxygen  is  taken  up,  indicating 
that  the  reaction  involved  is  one  of  oxidation. 

Aminobenzoic  Acids. 

The  most  important  of  the  aminobenzoic  acids  is  o-amino- 
benzoic  add,  called  anthranilic  acid,  first  obtained  by  the  oxidation 
of  indigo  (404).  It  has  the  character  of  an  amino-acid,  yielding 
salts  with  both  acids  and  bases.  It  possesses  a  sweet  taste  and 
slightly  antiseptic  properties.  It  is  obtained  by  the  method  of 
HOOGEWERFF  and  VAN  DORP  (259),  by  treating  phthalimide  with 
bromine  and  potassium  hydroxide.  The  potassium  salt  of  phthal- 
aminic  acid  is  first  formed,  and  then  changes  into  anthranilic  acid  : 

NH2 


Phthalimide  Potassium  phthalaminate  Anthranilic  acid 


476  ORGANIC  CHEMISTRY.  [§347 

Anthranilic  acid  melts  at  145°,  and  by  careful  heating  can  be 
sublimed  without  decomposition.  When  strongly  heated,  it 
decomposes  to  a  considerable  extent  into  carbon  dioxide  and 
aniline.  It  dissolves  in  water  and  readily  in  alcohol.  By  the 
method  indicated  it  is  prepared  technically  for  the  synthesis  of 
indigo,  bleaching-powder  being  substituted  for  the  potassium 
hydroxide  and  bromine.  Its  methyl  ester  causes  the  fragrance 
of  many  flowers.  It  has  a  powerful,  but  agreeable,  odour,  and 
finds  application  in  the  perfume-industry. 


Phthalic  Acid. 

347.  Phthalic  acid  is  the  or^o-dicarboxylic  acid  of  benzene,  and 

POOTT  1 
has  the  formula  C6H4  <QQQJJ  o-     It  is  obtained  by  the  oxidation 

of  aromatic  hydrocarbons  with  two  side-chains  in  the  ortho- 
position,  or  their  derivatives  with  substituents  in  the  side-chains. 
It  is  worthy  of  note  that  chromic  acid  cannot  be  employed  in  this 
oxidation,  since  it  decomposes  or^o-derivatives  completely  into 
carbon  dioxide  and  water.  Phthalic  acid  is  employed  in  ths 
preparation  of  artificial  indigo  (405),  and  is  manufactured  by  oxi- 
dizing naphthalene  (377),  CioHg,  by  heating  with  very  concen- 
trated sulphuric  acid. 

,  Phthalic  acid  is  crystalline,  and  dissolves  readily  in  hot  water, 
alcohol,  and  ether.  It  has  no  definite  melting-point,  since  on 
heating  it  loses  water,  yielding  phthalic  anhydride,  which  sublimes 
in  beautiful,  long  needles  : 


- 

Phtlialic  anhydride 

If  they  followed  the  ordinary  course   of  the  reaction  form- 
ing  acid   chlorides,   phosphorus  pentachloride  and  phthalic  acid 

CO01 
would  react  to  produce  a  chloride  of  the  constitution  C6H4  < 


/CC12 
/ 


That  they  do   not  and   that  phthalyl  chloride  has  the  structure 

C6H 


4 

Nco 


§348]  PHTHALIC  ACID.  477 

can  be  proved  in  various  ways.  When  aluminium  chloride  reacts 
with  phthalyi  chloride  in  presence  of  benzene,  there  results  a  com- 
pound with  the  formula 


>0        . 
XCO 

called  phthalophenone,  the  constitution  of  which  follows  from  its 
formation  by  the  elimination  of  water  from  triphenylcarbinolcar- 
boxylic  acid: 

CH 


C6H4<       X) 


i 


-  H20  =  C6H4<    >  O 


CO 
OH 

Triphenylcarbinol-  Phthalophenone 

carboxylic  acid 

Another  proof  of  the  constitution  indicated  above  for  phthalyi 
chloride  is  the  fact  that  reducing  agents,  such  as  sodium-amalgam 
and  water,  or  zinc  and  hydrochloric  acid,  cause  the  replacement  of 
its  halogen  atoms  by  hydrogen,  with  formation  of  phthalide.  This 
substance  has  no  aldehydic  properties,  but  has  the  constitution 


>  O,  since  on  treatment  with  sodium  hydroxide  or  dilute 
O 
acids  it  yields  o-hydroxymethylbenzoic  acid: 


/CHo  /CH2OH 

C6H4<     >0  +  H     =C6H4< 

XCO         OH  XCOOH 


By  elimination  of  water,  this  acid  is  reconverted  into  phthalide. 
These  transformations  prove  phthalide  to  be  a  lactone,  and  not  a 

PHO 

dialdehyde,  CeH4  <^JTQ,  as  it  should  be  if  the  formula  of  phthalyi 

C-iloride  were  C6H4  <QQQ- 

348.  The  oxygen  of  the  carbonyl-group  in  phthalic  anhydride 
can  also  participate  in  other  reactions.  Thus,  when  this  sub- 
stance is  heated  with  phenols  and  sulphuric  acid,  phthaleins  are 
formed : 


478  ORGANIC  CHEMISTRY.  {§  348 

/C6H4OH 
/C^-C6H4OH 
=  H20+C6H4<     >0 

co-  Xco 

Phthalic  anhydride  Phenolphthaleln 

Phenolphthalem,  the  simplest  member  of  the  phthalein  series, 
is  a  yellow  powder.  On  account  of  its  phenolic  character  it  dis- 
solves in  alkaline  solutions,  with  formation  of  a  fine  red  colour,  and 
is  a  sensitive  indicator  for  alkalimetry. 

Resorcinolphthaleln  or  -fluorescein  is  characterized  by  the  display 
of  an  intense  yellowish-green  fluorescence  in  alkaline  solution.  It 
owes  its  name  to  this  property,  which  affords  a  delicate  test  for 
phthaiic  anhydride,  phthalic  acid,  and  resorcinol,  since  fluorescence 
is  exhibited  by  mere  traces  of  fluorescein.  It  is  prepared  by  heating 
together  resorcinol  and  phthalic  anhydride  at  210°,  in  presence  of 
zinc  chloride  as  a  dehydrating  agent.  On  treatment  with  bromine, 
fluorescein  yields  tetrabromo  fluorescein: 

,C6HBr2(OH) 


}HBr2(OH) 

.A 

CO 

Its  potassium  derivative,  C20H605Br4K2,  is  the  beautiful  dye  eosin. 
The  constitution  of  the  phthalems  is  inferred  from  their  being 
convertible  into  derivatives  of  triphenylmethane  (373). 

In  the  preparation  of  phenolphthalem  a  by-product,  fluoran, 
insoluble  in  alkalis  is  formed.  According  to  the  researches  of  R. 
MEYER,  this  substance  has  the  formula 

/C0\ 
C6H4<        >0 


C6H4\       SO  >  /  \* 


C/ 

-fo 

I.  II. 

in  which  the  two  phenol-residues  are  united  at  the  ortho-positions  to 
the  phthalie-anhydride-residue,  and  not  at  the  para-positions,  as  in 
phenolphthalem.  Fluoran  contains  the  pyrone-nucleus, 


c 
c" 


§  349]  PHTHALIMIDE.  479 

R.  MEYER  has  pointed  out  that  many  derivatives  containing  this 
nucleus  fluoresce.  He  proved  that  fluorescein  is  dihydroxyfluoran, 
with  the  formula 

CO. 
C.H  '       )0 

\  c/ 


HoC^jxJvJoH 

O 

JCO 

349.  Phthalimide,  CeH^  >  NH,  is  of  importance  on  account 


of  its  application  to  the  synthesis  of  primary  amines  with  sub- 
stituted alkyl-groups.  It  is  obtained  by  passing  dry  ammonia 
over  heated  phthalic  anhydride.  The  imi  no-hydrogen  is  replace- 
able by  metals  :  thus,  the  potassium  compound  is  precipitated  by 
the  action  of  potassium  hydroxide  on  the  alcoholic  solution  of  the 
imide.  When  potassium  phthalimide  is  treated  with  an  alkyl 
halide,  the  metal  is  replaced  by  alkyl:  on  heating  with  acids  or 
alkalis,  a  primary  amine,  free  from  secondary  and  tertiary  amines, 
is  produced  : 

/CO    _  /CO 

C6H4<    >N[K+Br.jCnH2n+1  ->C6H4<     >N.CnH2n+1  -» 
XX)  XX) 

Potassium  phthalimide 

—  >  C6H4  <  +  NH2  •  CnH2n  +1  . 


Alkyl  halides  with  various  substituents  can  be  employed  in  this 
reaction:  thus,  from  ethylene  bromide,  CH2Br«CH2Br,  is  obtained 
bromoethylamine,  NH2-CH2-CH2Br  ;  from  ethylenebromohydrin, 
CH2Br.CH2OH,  hydroxyethylamine,  NH2.CH2-CH2OH;  etc. 

Another  example  is  EMIL  FISCHER'S  synthesis  of  ornithine  (243). 
Potassium  phthalimide  is  brought  into  contact  with  trimethylene 
bromide: 

CH2Br  -> 
>  N  •  CH2.CH2.CH2Br. 


480  ORGANIC  CHEMISTRY.  [§  350 

The  compound  obtained  is  treated  with  diethyl  monosodiomalonate, 

ro 
and  yields  C6H4<^>N.CH2-CH2.CH2.CH(COOC2H5)o,  the  ter- 

tiary hydrogen  atom  of  which  can  be  substituted  by  bromine. 
Saponitication  and  elimination  of  CO2  give 

C6H4  <  £Q  >  N  •  CH2  -  CH2  -  CH2  •  CHBr  .  COOH. 

By  heating  with  aqueous  ammonia,  Br  is  then  .replaced  by  NH2. 
Subsequent  heating  with  concentrated  hydrochloric  acid  yields 
ornithine: 


+2OHH 
£        J+H2N.CH2.CH2.CH2.CH(NH2).COOH. 

Ornithine 

These  examples  make  it  evident  that  this  method  can  be  ap- 
plied to  the  preparation  of  the  most  variously  substituted  primary 
amines. 

HOOGEWERFF  and  VAN  DORP  found  that  ammonia  reacts  with 

ON 

phthalyl    chloride,    yielding    o-cyanobenzoic    acid,    C6H4 


It  must  be  assumed  that  an  isoimide  of  phthalic  acid  is  formed  as 
an  intermediate  product  : 

CC12  /C=NH  /CN 

4<:    >  0  -»  C6H/  >  0      -*  C6H/ 
XCO  XCO  XCOOH. 

Phthalyl  tsolmide  o-Cyanobenzoic 

chloride  acid 

Although  they  have  not  been  able  to  isolate  the  iso-imide  itself,  they 
have  prepared  a  number  of  derivatives  in  which  the  imino-hydrogen 
is  replaced  by  hydrocarbon-residues. 

isoPhthalic  and  Terephthalic  Acids,  C6H4(COOH)2  (1:3)  and  (U4). 

350.  isoPhthalic  acid  can  be  obtained  by  the  oxidation  of  com- 

-   pounds  with  two  side-chains  in  the  raeta-position,  and  also  by  the 

oxidation  of  resin  (colophonium)  with  nitric  acid.     It  dissolves  with 

difficulty  in  water,  and  does  not  yield  an  anhydride.     Symmetrical 

methylisophthalic  acid  is  mentioned  in  231. 


351]  SUBSTITUTRD   ALDEHYDES.  481 

Terephthalic  acid  can  be  prepared  by  several  methods;  for  example, 
by  the  oxidation  of  turpentine.  It  is  almost  insoluble  in  water, 
alcohol,  and  ether.  It  does  not  melt  at  the  ordinary  pressure,  but 
at  high  temperatures  sublimes  without  decomposition.  Like  iso- 
phthalic  acid,  it  does  not  form  an  anhydride. 

Higher  Polybasic  Acids. 

Tricarboxylic,  tetracarboxylic,  pentacarboxylic,  and  hexacar- 
boxylic  acids  are  known.  The  most  remarkable  is  the  hexacar- 
boxylic  mellitic  acid,  a  constituent  of  the  mineral  honey-stone,  found 
in  brown-coal  seams.  Honey-stone  is  the  aluminium  salt  of  mellitic 
acid,  and  has  the  formula  C12O12A12  +  18H2O  :  it  forms  yellow  quad- 
ratic octahedra.  Mellitic  acid  is  produced  by  the  oxidation  of  wood- 
charcoal  with  an  alkaline  solution  of  potassium  permanganate. 
It  crystallizes  in  fine  needles,  and  dissolves  freely  in  water  and  alco- 
hol. On  heating,  it  loses  two  molecules  of  carbon  dioxide  and  two 
molecules  of  water,  with  formation  of  pyromellitic  anhydride, 

CO        1 


C0>05 
which  takes  up  water,  and  yields  pyromellitic  acid,  C6H2(COOH)4. 

VIII.    SUBSTITUTED  ALDEHYDES. 

351.  m-Nitrobenzaldehyde  is  the  main  product  formed  in  the 
nitration  of  benzaldehyde,  o-nitrobenzaldehyde  being  a  by-product 
in  the  reaction.  The  best  mode  of  preparing  the  ortho-compound 
is  to  oxidize  o-nitrotoluene  with  manganese  dioxide  and  sulphuric 
acid.  In  sunlight  it  is  rapidly  transformed  into  o-nitrosobenzo'ic 
acid: 


/N02  y 

C6H4<(  ->     C6H4/ 

XCHO  XCOOH 

Hydroxy  aldehydes. 

Hydroxyaldehydes  can  be  obtained  artificially  by  a  synthetical 
method  generally  applicable  to  the  preparation  of  aromatic 
hydroxy  aldehydes.  It  consists  in  treating  the  phenols  in  ethereal 


482  ORGANIC  CHEMISTRY.  [§  351 

solution  with  anhydrous  hydrocyanic  acid  and  hydrochloric-acid 
gas,  it  being  sometimes  an  advantage  to  add  a  small  quantity  of 
zinc  chloride  as  a  condensing  agent.  This  mode  of  synthesis  was 
discovered  by  GATTERMANN,  whose  name  it  bears.  The  hydro- 
chloride  of  an  imide  is  formed  as  an  intermediate  product,  and  can 
sometimes  be  isolated : 

C6H5OH+HCN+HC1 

On  treatment  with  warm  water,  the  imide-salt  is  converted  into 
the  hydroxyaldehyde  and  ammonium  chloride: 

=  C6H4<CHO+NH4C1. 


p-Hydroxybenzaldehyde  is  here  obtained  from  phenol. 

/OH     ! 
Salicylaldehyde,  CeH^   /H    ,  occurs  in  volatile  oil  of  spircea. 


It  can  be  prepared  artificially  by  REIMER'S  synthesis,  another 
reaction  generally  applicable  to  the  production  of  aromatic 
hydroxyaldehydes,  and  depending  on  the  action  of  chloroform 
and  potassium  hydroxide  on  phenols: 


/OH 
C6H4< 

~|H  +  C1|CHC12  NVyO 

Salicylaldehyde 

The  o-hydroxyaldehydes  colour  the  skin  deep  yellow. 
To  this  class  of  substances  belongs  vanillin, 


C6H3(-OCH3  3' 

NOH    4 

the  methyl  ether  of  protocatechualdehyde.  It  is  the  aromatic  prin- 
ciple of  vanilla,  and  is  prepared  on  the  large  scale  by  oxidizing 
isoeugenol, 

/OH 
f  OCH3 
\CH:CH.CH3 


§  352]  HYDROXY ALDEHYDES.  483 

This  substance  is  obtained  by  boiling  eugendL, 


v     w^-LJ-g  , 

\CH2.CH:CH2 

with  alcoholic  potash,  which  alters  the  position  of  the  double  link- 
ing in  the  side-chain.  Eugenol  is  the  chief  constituent  of  oil  of 
cloves. 

Vanillin  has  been  synthesized  by  REIMER'S  method,  the  action 
of  chloroform  and  sodium  hydroxide  on  guaiacol  (336) : 

[OH]  PH 

CHC12  CH<£B  C0 


r» 


OCH3  " 
OH  OH  OH  OH 


Intermediate  products  Vanillin 

Piperonal  is  mentioned  in  353. 

IK.    POLYSUBSTITUTED   BENZENE  DERIVATIVES  WITH  SUBSTIT- 
UENTS  IN  THE  SIDE-CHAIN. 

OTT 
352.  p-Hydroxyphenylpropionic  acid,  CeH4<Qjj  ^jj  -COOK 

is  of  some  importance  owing  to  its  relation  to  tyrosine  (M.  P.  235°), 
which  derives  its  name  from  its  presence  in  old  cheese  (Greek,  rupos), 
and  is  produced  when  proteins,  such  as  white  of  egg,  horn,  hair,  etc., 
are  boiled  with  hydrochloric  acid  or  sulphuric  acid.  Its  formula  is 

/H 
CgHnOsN,  and  its  structure  HO  •  C6H4  -  CHo  .  C^-COOH  ;  it  is  the 

\NH2 

a-amino-acid  of  p-hydroxyphenylpropionic  acid.  Being  an  amino- 
acid,  it  yields  salts  with  acids  as  well  as  with  bases. 

OTT 
o-Hydroxycinnamic  acid,  C6H4  <..J  exists  in  two 


forms,  coumaric  acid  and  coumarinic  acid,  which  are  easily  converted 
into  each  other.  Coumarinic  acid  is  not  known  in  the  free  state, 
but  only  in  the  form  of  salts,  since,  on  liberation,  it  at  once  loses  a 


484  ORGANIC  CHEMISTRY.  [§  353 

molecule  of  water,  yielding  coumarin,  the  aromatic  principle  of 
woodruff  (Asperula  odorata).  Coumaric  acid,  on  the  other  hand, 
does  not  yield  a  corresponding  anhydride:  removal  of  water  pro- 
duces coumarin,  which  is  converted  into  salts  of  coumarinic  acid  by 
treatment  with  alkalis.  This  behaviour  recalls  that  of  fumaric  acid 
and  male ic  acid  (169) ,  and  it  may  be  assumed  that  the  stereoisomer- 
ism  of  these  acids  is  similar.  Both  can  then  be  represented  as 
follows : 

H.C.C6H4.OH    H.C-C6H4.OH  H.C.C6H4 


-H20  = 
•C.C< 


HOOC-C-H  H.C.COOH  H-C-CO 

Coumaric  acid;  Coumarinic  acid;  Coumarin 

gives  no  corresponding  only  known  in  the  form 

anhydride  of  salts 

.   Coumarin  can  be  obtained  from  salicylaldehyde  by  SIR  WILLIAM 
PERKIN'S  synthesis  (328)  :  acetylcoumaric  acid, 


PH  /°IC 


CH:CH.CO|OH' 

is  first  formed,  and  is  converted  into  coumarin  by  heating,  acetic 
acid  being  eliminated. 

353.  The  unsaturated  piperic  acid,  or  Sil-methylenedihydroxy- 
cinnamenylacrylic  acid,  Ci2H10O4,  is  a  decomposition-product 
of  piperine  (390).  Oxidation  converts  piperic  acid  into  piperonal 
or  heliotropin, 


CH:CH.CH:CH-COOH 


Piperonal 


The  constitution  of  this  substance  is  established  by  two  reactions. 
First,  on  heating  with  hydrochloric  acid  it  is  converted  into  proto- 
catechualdehyde  and  carbon: 


CHO-C6H3  <>  CH2  =  CHO.C6H3 


§  353]  PIPERONAL  AND  ADRENALINE.  485 

Second,  it  is  regenerated  by  the  action  of  methylene  iodide  and 
alkali  upon  this  aldehyde. 

Piperonal  melts  at  37°,  and  boils  at  263°;  its  odour  exactly 
reembles  that  of  heliotropes.  In  presence  of  caustic  soda, 
piperonal  condenses  with  acetaldehyde  to  piper  onylacr  aldehyde  : 


Q>C6H3«CQ  +CH3»CQ 


+H2O. 


By  PERKIN'S  synthesis  (328),  piperonylacraldehyde  is  con- 
verted by  the  action  of  sodium  acetate  and  acetic  anhydride  into 
piperic  acid: 

CH2<Q>C6H3-CH:CH.CQ+CH3-COOH  = 
=  CH2<o>C6H3.CH:CH.CH:CH.COOH  +  H2O. 


Adrenaline  or  suprarenine,  CgH^ON,  is  prepared  from  the 
suprarenal  capsules  of  the  horse  and  other  animals.  It  is  char- 
acterized by  its  powerful  haemostatic  properties.  On  oxidation, 
it  yields  protocatechuic  acid,  and  on  distillation  with  sodium 
hydroxide,  methylamine.  With  benzoyl  chloride  it  forms  a  tri- 
benzoyl  derivative. 

It  is  prepared  by  a  synthetic  method.  Chloroacetyl  chloride 
reacts  with  catechol  (I.)  to  form  chloroacetylcatechol  (II.).  On 
treatment  with  methylamine,  this  substance  yields  an  amino- 
ketone  (III.),  reducible  to  adrenaline  (IV.)  • 


Jl     HO/  >CO,CH2.NH.GH3 

n.  I        ->  m. 

HOI     J  HOi 


CH2  •  NH  •  GH3 

IV. 

H°\/ 

Adrenaline 


486  ORGANIC  CHEMISTRY.  [§  353 

Many  organic  bases  of  phenolic  character  have  valuable  phar- 
macological properties.     Other  types  of  this  class  are  hordenine, 

4  1 

HO •C6H4'CH2 •CH2'N(CH3)2,  present  in  germinating  barley;  and 
p-hydroxyphenylethylamine,  HO  •  CeH*  •  NH  •  C2H8,  the  active  principle 
of  ergot. 


ORIENTATION  OF  AROMATIC  COMPOUNDS. 

354-  Orientation  is  the  determination  of  the  relative  positions 
occupied  by  the  side-chains  or  substituents  in  the  benzene-ring. 
A  description  of  a  number  of  the  most  important  substitution- 
derivatives  of  benzene  having  been  given  in  the  foregoing  pages,  it 
becomes  necessary  to  furnish  an  insight  into  the  methods  by  which 
orientation  is  carried  out. 

These  methods  are  based  on  two  main  principles. 

1.  Relative  determination  of  position. — The  compound  with  sub- 
stituents in  unknown   positions   is   converted   into   another  with 
known  positions,  it  being  inferred  that  the  first  compound  has  its 
substituents  arranged  similarly  to  the  second.     If,  for  example,  the 
constitution  of  one  of  the  three  xylenes  is  required,  the  hydrocarbon 
can  be  oxidized.     The  particular  phthalic  acid  formed  indicates  the 
positions  of  the  methyl-groups  in  the  xylene  under  examination, 
provided  the  positions  of  the  carboxyl-groups  in  the  three  phthalic 
acids  are  known. 

To  apply  this  method,  it  is  necessary  to  know  the  positions  of 
the  substituents  in  a  small  number  of  compounds,  and  it  is  further 
assumed  that  the  positions  of  the  substituents  remain  the  same 
during  the  course  of  the  reactions  involved.  Usually,  this  continu- 
ity holds,  although  the  position  of  the  side-chain  does  alter  in  a  few 
reactions  (332). 

To  avoid  erroneous  conclusions,  it  is,  therefore,  desirable  in 
cases  of  doubt  to  check  the  determination  of  position  by  convert- 
ing the  substance  into  another  compound. 

2.  Absolute  determination  of  position. — The   positions   of  the 
substituents  are  determined  without  the  aid  of  other  compounds 
with    substituents   in  known    positions.     A   general    method    is 
afforded  by  KORNER'S  principle,  by  which  it  is  possible  to  ascer- 
tain whether  substances  C6H4X2,  containing  two  substituents,  are 

487 


488  ORGANIC  CHEMISTRY.  [§  355 

or^o-compounds,  w^a-compounds,  or  para-compounds,  effected 
by  determining  the  number  of  trisubstitution-products  correspond- 
ing with  them. 

When  a  third  group,  Y,  is  introduced  into  an  or/^o-compound, 
C6H4X2,  whether  Y  is  the  same  as  or  different  from  X,  only  two 
isomerides  can  be  formed, 

X 

/\x 

and        |       |. 

\/ 
Y 

The  introduction  of  a  third  group  into  a  raeta-compound  renders 
possible  the  formation  of  three  isomerides, 


and 


With  a  para-compound  the  introduction  of  a  third  group  yields 
only  one  trisubstitution-product, 


In  addition  to  this  general  method,  there  are  other  special 
methods,  several  of  which  are  described.  They  substantiate  fully 
the  conclusions  already  arrived  at  by  KORNER'S  method. 

i.  Absolute  Determination  of  Position  for  ortho -Compounds. 

355.  For  the  or^o-series,  the  structure  of  a  dibromobenzene 
melting  at  5-6°  is  determined  by  means  of  KORNER'S  principle: 
this  body  yields  two  isomeric  nitrodibromobenzenes.  The  con- 
stitution of  a  xylene  boiling  at  142°  and  melting  at  —  28°  has  also 
been  established  by  this  method :  it  gives  rise  to  two  isomeric 


§355] 


ORIENTATION. 


489 


nitroxylenes  when  treated  with  nitric  acid.  This  xylene  is  con- 
verted into  phthalic  acid  by  oxidation,  proving  that  the  latter  is 
an  or^o-compound. 

The  oxidation  of  naphthalene  (377),  Ci0H8,  to  phthalic  acid  also 
proves  that  the  carboxyl-groups  of  this  acid  are  in  the  ortho-posi- 
tion.  This  reaction  indicates  that  the  structure  of  naphthalene 
must  be  C6H4  <  C4H4,  the  group  C4H4  being  linked  to  two  positions 
in  the  benzene-ring.  When  naphthalene  is  treated  with  nitric  acid, 
nitronaphthalene  is  formed,  and  is  converted  by  oxidation  into 
nitrophthalic  acid.  The  group  C4H4  has,  therefore,  been  converted 
into  two  carboxyl-groups: 


N02  -  C6H3  <  C4H4 

Nitronaphthalene 


N02  •  C6H3  < 

Nitrophthalic  acid 


If,  however,  the  nitro-group  is-  reduced,  and  the  aminonaphthalene 
thus  obtained  oxidized,  phthalic  acid  is  formed.  Hence,  the  group 
C4H4  forms  a  second  benzene-ring  with  the  two  carbon  atoms  of 
the  benzene-ring,  so  that  naphthalene  must  be  represented  by  the 
formula 


The  oxidation  of  nitronaphthalene  and  aminonaphthalene  fo 
expressed  by  the  scheme 


and 


NH2 


HOOC/N 


490  ORGANIC  CHEMISTRY.  [§  355 

Phthalic  acid  must,  therefore,  be  an  or^o-compound,  because 
if  it  be  assumed  to  have  the  raefa-structure,  for  example,  naphtha- 
lene must  be  represented  by  the  formula 


\ 


which  involves  a  contradiction,  for  there  could  not  then  be  a  ben- 
zene derivative  produced  by  the  oxidation  of  both  nitronaphthalene 
and  aminonaphthalene. 

2.  Absolute  Determination  of  Position  for  weta-Compounds. 

356.  The  proof  that  mesitylene  is  symmetrical  trimethylbenzene 
(1:3:5)  is  stated  thus  by  LADENBURG. 
If  this  compound  has  the  constitution 

H 

CH3X\CH3 


the  three  hydrogen  atoms  directly  linked  to  the  benzene-ring  must 
be  of  equal  value.  If  this  can  be  proved,  the  structure  of  mesityl- 
ene is  established. 

The  proof  of  the  equality  is  as  follows.  On  nitrating  mesitylene  a 
dinitro-corapound  is  obtained.  If  the  hydrocarbon  is  represented  by 

I.    C6(CH3)3HHH, 
the  dinitro-compound  may  be  arbitrarily  assumed  to  be 

t  II.    C6(CH3)3N02N02H. 

One  of  the  nitro-groups  of  the  dinitro-compound  is  reduced,  and 
the  resulting  amino-compound  is  converted  into  an  acetyl-derivative* 
suppose  that  this  acetyl-derivative  is 

III.    C6(CH3)3N°02NH(C2H30)H. 
This  substance  can  be  again  nitrated,  when  there  must  result 


§  356]  ORIENTATION.  491 


It  is  possible  to  eliminate  the  acetylamino-group,  NH(C2H3O), 
from  this  compound  by  saponification,  subsequent  diazotization,  etc. 
A  dinitromesitylene  with  the  formula 

C6(CH3)3N02HNO2 

is  obtained,  identical  with  the  former  dinitro-product,  the  nitro- 
groups  of  which  are  at  a  and  b.    It  follows  that 


Nitromesidine,  a  :  b,  the  acetyl-compound  of  which  is  represented 
by  formula  III.,  furnishes  a  further  proof  that  Ha  =  Hc.  When  the 
ammo-group  is  eliminated  by  means  of  the  diazo-reaction,  there  is 
formed 

IV.    C6(CH3)3N02HH. 

This  substance  is  reduced,  and  converted  into  an  acetyl-compound, 
acetylmesidine, 

C6(CH3)3NH(C2H30)HH, 
which  can  be  again  nitrated,  yielding 

C6(CH3)3NH(C2H30)N02H. 

It  is  immaterial  whether  the  nitro-group  of  this  compound  is  at  b  or 
c,  since  the  equality  of  these  positions  relative  to  a  has  been  already 
proved. 

On  eliminating  the  acetylamino-group  from  the  last  substance, 
a  mononitromesitylene  is  produced,  identical  with  the  compound 
IV.  Hence,  a  =  b  =  c,  which  completes  the  proof  of  the  equality  of 
the  three  hydrogen  atoms. 

From  the  known  constitution  of  mesitylene  it  is  possible  to 
deduce  the  structure  of  many  other  compounds.  For  example, 
partial  oxidation  converts  it  into  mesitylenic  add; 

/COOH 
CeHs^CHs     , 
XCH3 

which  is  in  turn  converted  into  xylene  by  distillation  with  lime:  this 


492  ORGANIC  CHEMISTRY.  [§  357 

xylene  must  be  the  meta-compound.  Oxidation  converts  ra-xylene 
into  ^sophthalic  acid,  indicating  that  the  carboxyl-groups  in  the 
latter  occupy  the  raeta-position.  These  determinations  of  position 
have  been  fully  substantiated  by  the  application  of  KORNEK'S 
principle.  Thus,  NOLTIXG  has  prepared  three  isomeric  nitroxyl- 
enes,  in  which  the  relative  positions  of  the  methyl-groups  are  the 
same  as  in  the  xylene  obtained  from  mesitylenic  acid. 

Among  other  mda-compounds  in  which  the  position  of  the 
groups  has  been  independently  established,  is  a  dibromobenzene 
boiling  at  220°.  KORNER  proved  that  corresponding  to  this  sub- 
stance are  three  isomeric  tribromobenzenes  and  three  nitrodibromo- 
benzenes.  In  conclusion,  the  phenylenediamine  melting  at  62°  can 
be  obtained  from  three  different  diaminobenzoiic  acids  by  elimina- 
tion of  CO2,  so  that  it  also  must  be  a  meta-compound. 


3.  Absolute  Determination  of  Position  for  para-Compounds. 

357.  KORNEB'S  principle  has  been  of  great  service  in  determin- 
ing the  constitution  of  some  members  of  the  para-series.  For 
example,  from  the  xylene  boiling  at  138°,  and  melting  at  13°,  it  is 
only  possible  to  obtain  one  nitro xylene:  the  phenylenediamine 
melting  at  140°  can  only  be  obtained  from  one  diaminobenzoi'c  acid 
by  removing  CO2:  and  so  on. 

These  determinations  of  position  have  been  confirmed-  by 
another  method,  exemplified  by  the  identification  of  a  hydroxy- 
benzoic  acid  melting  at  210°  as  a  para-compound.  The  starting- 
point  of  the  proof  is  bromobenzoic  acid,  obtained  directly  by 
the  bromination  of  benzole  acid.  On  nitration,  two  isomeric 
nitrobromobenzoic  acids  are  formed,  either  of  which  yields  on 
reduction  the  same  aminobenzoic  acid,  anthranilic  acid.  This 
acid  can  be  converted  into  salicylic  acid  by  means  of  the  diazo- 
reaction.  It  follows  that  in  both  the  isomerides  the  nitro-group 
must  be  situated  symmetrically  to  the  car  boxy  1-group;  at  2  or  6, 
or  at  3  or  5,  if  the  carboxy  1-group  is  at  1.  The  same  reasoning 
establishes  the  position  of  the  hydroxy  1-group  in  salicylic  acid. 
The  bromine  atom  cannot  be  at  4,  because  two  isomeric  nitro-com- 
pounds  which  would  yield  the  same  aminobenzoic  acid  on  reduction 
could  not  be  obtained  from 


§  358]  ORIENTATION.  493 


The  bromine  atom  must,  therefore,  occupy  the  meta-position  or 
ort/io-position  to  the  carboxyl-group.  A  hydroxybenzoi'c  acid  melt- 
ing at  200°,  corresponding  with  this  acid  must  be,  therefore,  meta 
or  ortho.  Since  the  isomeric  salicylic  acid  can  also  be  only  a  meta- 
compound  or  an  or^o-compound,  there  remains  no  possibility, 
except  the  para-structure,  for  the  third  hydroxybenzoi'c  acid  melt- 
ing at  210°. 


Determination  of  Position  for  the  Trisubstituted  and  Higher- 
substituted  Derivatives. 

358.  This  orientation  can  usually  be  effected  by  ascertaining 
the  relation  in  which  they  stand  to  the  di-derivatives  of  known 
constitution.  For  example,  since  a  certain  chloronitroaniline, 
C6H3C1(NO2)(NH2),  is  obtained  by  nitrating  m-chloroaniline, 

NH2 

tor 

and  yields  p-chloronitrobenzene, 


Cl 

by  exchange  of  the  amino-group  for  hydrogen,  it  must  have  the 
constitutional  formula 

NH2 

N02 


A  more  complicated  example  of  orientation  is  afforded  by  the 
determination  of  the  positions  of  the  groups  in  picric  acid.  Careful 
nitration  converts  phenol  into  two  mononitrophenols, 


494  ORGANIC  CHEMI&TRY.  [§  358 


OH  OH 

N0>     and     s 

NO, 
M.P.  45°  M.P.  114° 

One  of  these  mononitrophenols  must  be  the  or^o-compound  and 
the  other  the  para-compound,  because  the  third  nitrophenol  can  be 
obtained  from  ra-dinitrobenzene — the  constitution  of  which  has  been 
proved  by  its  reduction  to  ra-phenylenediamine  (339) — by  reduction 
to  raeta-nitroaniline,  and  subsequent  exchange  of  NHa  for  OH  by 
diazotizing. 

When  further  nitrated,  both  nitrophenols  yield  the  same  dinitro- 
phenol,  which  can  therefore  only  have  the  formula 

OH 
NO2 


NO2 

The  mononitrophenol  melting  at  114°  is  converted  by  oxidation 
into  benzoquinone  (338),  and  must,  therefore,  be  the  para-com- 
pound. For-the  body  melting  at  45°  there  remains  only  the  ortho- 
structure.  On  nitration  this  o-nitrophenol  yields,  in  addition  to  the 
1  :2  :4-dinitrophenol  (OH  at  1),  another  dinitrophenol  with  its  groups 
at  1:2:6, 

OH 
N02(/\N02; 

for  on  conversion  of  this  into  its  methyl  ether,  and  heating  the  latter 
with  alcoholic  ammonia,  the  group  OCH3  is  replaced  by  NH2;  and 
this  substance,  which  has  the  formula 

NH 


is  converted  by  substitution  of  hydrogen  for  the  NH2-group  into 
the   ordinary   meto-dinitrobenzene.     Thus,   we   have   two   dinitro- 


phenols  of  known  structure, 


§359]     EQUIVALENCE  OF  BENZENE  HYDROGEN  ATOMS.       495 

rl 

V|N°2     and 


OH  OH 

)2,//X1N02 


NO, 


Further  nitration  converts  both  into  picric  acid,  which  must,  there 
fore.  have  the  constitution 

OH 


v 

NO2 

From  the  constitution  of  picric  acid  may  be  inferred  the  position 
of  the  groups  in  ordinary  trinitrobenzene,  since  this  compound  is 
readily  oxidized  to  picric  acid  (334).  This  trinitrobenzene  mustr 
accordingly,  have  the  symmetrical  structure. 

Equivalence  of  the  Six  Hydrogen  Atoms  in  Benzene. 

359.  It  is  stated  in  282  that  benzene  does  not  yield  isomeric 
mono-substitution-products,  and  the  inference  is  drawn  that  the  six 
hydrogen  atoms  of  this  hydrocarbon  are  of  equal  value. 

There  are  several  direct  methods  of  proving  this  equivalence,  one 
of  them,  devised  by  NOLTING,  being  characterized  by  its  simplicity. 
If  the  six  hydrogen  atoms  are  denoted  by  a,  b,  c,  d,  e,  and  /,  the 
ammo-group  in  aniline  may  be  arbitrarily  assumed  to  be  at  a.  When 
bromobenzene,  obtained  from  aniline  by  the  diazo-reaction  (307,  4), 
is  treated  with  methyl  iodide,  and  sodium  it  yields  toluene.  On 
nitration,  three  isomeric  nitrotoluenes  are  obtained  —  the  proportion 
of  the  raefa-compound  being  very  small.  In  these  compounds  the 
CH3  group  is  at  a,  so  that  the  nitro-groups  may  be  arbitrarily  assumed 
to  be  at  b,  c,  and  d  respectively.  On  reduction,  the  three  corre- 
sponding toluidines  result: 

C6H5-CH3(rt)  ->CH,-C.H4-NO,(&:c:d)  ->COOH.C6H4-NH2(6:c:rf). 

After  protection  of  the  amino-group  in  each  of  these  compounds 
by  acetylation,  the  three  aminobenzoic  acids  are  obtained  by 
oxidation.  These  acids  yield,  by  elimination  of  C02,  the  same 
aniline,  identical  with  the  original  substance.  It  follows  that 
a  =  b  =  c  =  d: 


496  ORGANIC  CHEMISTRY.  [8  360 


C6H6NH2  -*  C6H6Br 
a  a 


The  starting-point  of  the  proof  of  the  equivalence  of  e  and  /  to 
a,  6,  c,  and  d  is  o-toluidine,  in  which  the  CH3-group  may  be  assumed 
to  be  at  a,  and  the  NH2-group  at  b.  Nitration  of  its  acetyl-deriva- 
tive,  followed  by  elimination  of  the  acetyl-group,  produces  simul- 
taneously four  nitro-o-toluidines.  Since  a  and  b  are  occupied,  the 
nitro-groups  must  be  at  c,  d,  e,  and  /  respectively.  Replacement  of 
the  ammo-group  by  hydrogen  yields  four  nitrotoluenes,  a :  c,  a  :  d 
a  :  e,  and  a  :/.  The  first  two  are  m-nitrotoluene  and  p-nitrotoluene; 
they  are  also  obtained  by  direct  nitration  of  toluene,  as  described  in 
the  previous  paragraph.  The  nitrotoluene  a  :  e  is  identical  with  a  :  c, 
and  a  :  f  with  a  :  b,  which  indicates  the  equivalence  of  c  to  e  and  of 
6  to  /,  thus  completing  the  proof: 


CH36 
NH2a 


Influence  of  the  Substituents  on  Each  Other. 

360.  On  introduction  of  a  second  substituent  into  a  monosub- 
stituted  benzene  derivative,  CcH^X,  the  three  theoretically  possible 
di-derivatives  are  formed  in  very  unequal  proportion.  There 


§360]     INFLUENCE  OF  SUBSTITUENTS  ON  EACH  OTHER.    497 


are  two  main  types  of  substitution:  either  the  para-derivative 
and  the  or£/io-derivative  predominate;  or  the  meto-derivative 
constitutes  the  chief  product.  The  table  summarizes  the  most 
important  types  of  substitution,  the  numbers  in  brackets  indicat- 
ing the  by-products,  and  being  arranged  in  order  of  diminishing 
proportion. 


Element  or  Group'already 
present  (in  Position  1). 

Position  entered  by  Substituents. 

Cl 

Br 

I 

S03H 

N02 

ci 

4(2)  (3) 
4(2)  (3) 

4(2) 

3 

4(2) 
4(2) 
3 

4(2)  (3) 
4(2)  (3) 
4 
4(2) 
3 
3 

4(2) 
3 

4 

4 

4(2) 

4 

4(2) 
3 

4 
4 

4 

4(2) 
3(4) 
3(2)  (4) 
4(2) 
4(2)  (3) 
3(4) 

4(2) 
4(2) 
4(2) 
4(2) 
3(2)(4) 
3(2)(4) 
4(2) 
4(2)  (3) 
3(2)  (4) 
3 

Br                      

I               

OH 

SO3H 

NO2                              

NH2                    

CH3                       

COOH       

CN       

The  table  indicates  that  a  second  substituent  is  directed  into 
the  para-position  and  the  or^o-position  by  the  presence  of  halogens 
and  the  groups  hydroxyl,  amino,  and  methyl;  but  into  the  meta- 
position  by  the  groups  sulpho,  nitro,  carboxyl,  and  cyano.  In 
both  instances  the  influence  is  exerted  independently  of  the 
nature  of  the  substituent  introduced.  This  rule  is  of  general 
application,  and  is  known  as  the  ride  of  the  constancy  of  substitu- 
tion-type. 

The  relative  proportions  in  which  the  isomerides  are  formed 
vary  greatly  even  for  the  same  type  of  substitution,  and  depend 
on  three  factors:  (1)  the  substituent  already  present;  (2)  the 
substituent  introduced;  (3)  the  experimental  conditions. 
These  three  factors  are  powerless  to  modify  the  substitution- 
type,  which  is  almost  invariable;  but  they  cause  important 
changes  in  the  proportions  of  the  isomerides  formed  in  each  type. 
A  few  examples  illustrating  this  influence  are  subjoined. 

1.  Nitration  at  0°  of  fluorobenzene  yields  12  •  4  per  cent,  of 
the  oH/io-nitro-product,  and  87*6  per  cent,  of  the  para-nitro- 


498  ORGANIC  CHEMISTRY.]  [§  361 

product.  Nitration  at  the  same  temperature  of  chlorobenzene 
produces  30  •!  per  cent,  of  o-chloronitrobenzene,  and  69-9  per 
cent,  of  p-chloronitrobenzene. 

2.  The  chlorination  at  90°  of  phenol  gives  50 -2  per  cent,  of 
p-chlorophenol,  and  49 -S  per  cent,  of  o-chlorophenol.     Bromina- 
tion  under  the  same  conditions  yields  90*7  per  cent,  of  p-bromo- 
phenol,  and  9-3  per  cent,  of  o-bromophenol.     These  percentages 
indicate  the  great  influence  exerted  by  the  substituent  introduced 
•on  the  proportion  of  the  isomerides  formed,  even  when  these 
substituents  are  as  similar  as  chlorine  and  bromine. 

3.  Temperature  is  one  of  the  important  factors  in  the  experi- 
mental  conditions.      In   nitration-processes   it   exerts   no   great 
influence  on  the  proportion  of  the  isomerides.     At  —30°,  nitra- 
tion of  benzoi'c  acid  gives  14  •  4  per  cent,  of  o-nitrobenzoic  acid, 
85  «0  per  cent,  of  ??^-nitrobenzolc  acid,  0-6  per  cent  of  p-nitro- 
benzoic  acid;    at  30°,  the  corresponding  percentages  are  22-3, 
76-5,   and   1«2.     The  temperature   can  exert  a  very  important 
influence  on  the  course  of  sulphonation-processes.     Sulphonation 
of  toluene  at  0°  with  excess  of  sulphuric  acid  gives  53  •  5  per  cent, 
of  p-toluenesulphonic  aci'd,  3-8  per  cent,  of  m-toluenesulphonic 
acid,   and  42 •  7   per  cent,   of  o-toluenesulphonic   acid;    for   sul- 
phonation  at  100°  the  corresponding  percentages  are  72  •  5,  10-1, 
and  17-4. 

In  halogenation-processes  the  nature  of  the  catalyst  influences 
the  proportion  of  the  isomerides  formed.  The  chlorination  of 
chlorobenzene  with  0-5  per  cent,  of  aluminium  chloride  as  catalyst 
yields  65-7  per  cent,  of  p-dichlorobenzene,  29-6  per  cent,  of 
o-dichlorobenzene,  and  4»7  per  cent,  of  m-dichlorobenzene;  with 
an  equivalent  proportion  of  ferric  chloride  as  catalyst  the  cor- 
responding percentages  are  55-5,  39  •  2,  and  5-3. 

361.  The  introduction  of  a  third  substituent  C  into  a  benzene 
derivative  CbH^AB  raises  an  interesting  problem:  knowing  the 
isomerides  formed  by  the  introduction  of  C  into  C6H5A  and  C6H5B 
respectively,  and  the  proportion  of  each,  is  it  possible  to  predict 
the  isomerides  C6H3ABC  formed  by  the  introduction  of  Cinto 
CelliAB,  and  the  proportion  of  each? 

In  a  qualitative  sense  prediction  is  possible,  but  the  problem  is 
much  more  complex  than  a  superficial  consideration  indicates. 
For  a  benzene  derivative  C6H4AB  with  formula  I., 


3611   INFLUENCE  OF  SUBSTITUENTS  ON  EACH  OTHER.       499 
Apo 


I. 

in  which  both  A  and  B  direct  substitution  to  the  or^o-position  and 
para-position,  the  entrance  of  the  third  substituent  would  be  expected 
to  take  place  at  4  and  6  under  the  influence  of  A,  and  at  3  and  5 
under  the  influence  of  B;  that  is,  the  formation  of  the  four  possible 
isomerides  would  be  anticipated.  Similarly,  in  combination  II., 
in  which  Bra  indicates  direction  by  B  of  a  new  substituent  to  the 
meta-position,  A  would  be  expected  to  direct  a  new  substituent 
to  positions  2,  4,  and  6,  and  B  to  direct  it  to  position  5.  In  actual 
practice,  the  relations  are  much  more  complex,  although  there  are 
instances  of  the  formation  of  the  four  isomerides,  exemplified  by 
o-chlorotoluene,  corresponding  with  formula  I.  In  other  examples 
such  as  that  of  o-cresol, 

OH 


substitution  takes  place  at  positions  4  and  6  only;  while  with 
compounds  of  type  II.  substitution  at  position  5  has  never  been 
observed. 

The  explanation  must  be  that  the  velocities  of  the  substitution 
induced  by  the  substituents  already  present  have  very  divergent 
values.  Assuming  the  velocity  of  substitution  due  to  the  hydroxyl- 
group  in  o-cresol  to  be  a  hundred  times  as  great  as  that  due  to  the 
methyl-group,  the  extent  of  substitution  at  positions  3  and  5  would 
be  so  small  as  to  render  detection  of  the  products  impossible.  The 
conclusion  is  also  inevitable  that  in  compounds  of  type  II.  sub- 
stitution is  much  more  rapid  at  the  para-position  and  the  ortho- 
position  than  at  the  raeZa-position. 

A  study  of  the  different  examples  of  substitution  in  compounds 
C6II4AB,  and  a  quantitative  estimation  of  the  isomerides  formed, 
enable  the  velocities  induced  by  the  various  substituents  to  be 
arranged  in  order,  although  in  almost  all  instances  the  attainment 
of  such  an  arrangement  by  direct  determination  is  precluded.  The 


500  ORGANIC  CHEMISTRY.  [§  362 

groups  causing  substitution  at  the  para-position  and  the  ortho- 
position  exert  their  influence  in  the  order 

OH>  NH2>  halogens  >  CH3; 

and  the  much  less  powerful  groups  causing  substitution  at  the 
meto-position  in  the  order 

COOH>S03H>NO2. 

Inversely,  knowing  these  orders  of  velocity,  it  is  possible  to  predict 
the  isomerides  obtainable  in  a  given  reaction;  thus,  in  chloro- 
phenol  the  substituent  would  be  introduced  mainly  at  the  ortho- 
position  and  the  para-position  to  hydroxyl;  but  in  chlorobenzo'ic 
acid  chiefly  in  the  or^o-position  and  para-position  to  chlorine. 

362.  This  opposition  between  or^o-derivatives  and  para- 
derivatives  on  the  one  hand,  and  weta-derivatives  on  the  other,  is 
not  only  observed  in  their  preparation,  but  also  in  many  of  their 
properties.  As  a  class,  the  weta-compounds  are  more  stable 
towards  reagents  than  the  or^o-derivatives  and  para-derivatives. 
An  example  is  given  in  331. 

OrZ/io-groups  sometimes  exert  a  remarkable  influence  in 
retarding  or  partially  preventing  reactions  which  take  place 
readily  in  their  absence.  The  following  reactions  exemplify  this 
phenomenon. 

When  an  acid  is  dissolved  in  excess  of  absolute  alcohol  it  can  be 
almost  quantitatively  converted  into  an  ester  by  passing  a  current 
of  hydrochloric-acid  gas  through  the  mixture  (93,  1).  VICTOR 
MEYER  and  his  students  found,  however,  that  esterification  of  acids 
containing  two  groups  in  the  or^o-position  relative  to  carboxyl, 

COOH 


could  not  be  thus  effected.  On  the  other  hand,  when  the  acid 
has  been  converted  into  an  ester  (by  means  of  the  silver  salt  and 
an  alkyl  halide)  the  ester  so  formed  can  only  be  saponified  with 
difficulty.  When  the  two  substituents  occupy  any  of  the  other 
positions,  these  peculiarities  do  not  manifest  themselves,  or  at  least 


§  362]     INFLUENCE  OF  SUBSTITUENTS  ON  EACH  OTHER.    501 

not  to  the  same  extent.     Ketones  substituted  in  the  two  artho- 
positions, 


CH 


where  R  is  an  alkyl-radical,  cannot  be  converted  into  oximes, 
wherein  they  differ  from  all  other  ketones.     o-o-Dimethylaniline, 


CH3 

> 

CH 


is  not  converted  by  treatment  with  an  alkyl  iodide  into  a  quater- 
nary salt.  Pentamethylbenzonitrile,  C6(CH3)5CN,  cannot  be  hy- 
drolyzed  to  the  corresponding  acid.  The  methyl-hydrogen  in  o-o- 
dinitrotoluene, 

/N022 

(_;6H3\~C-H3  1, 

XNO26 

cannot  be  replaced  by  halogens  even  at  a  high  temperature  (200°), 
as  is  also  true  of  1 : 2 : 4-dinitrotoluene.  In  spite  of  numerous 
attempts,  the  hydrolysis  of  o-mtrosalicylonitrile, 


to  the  corresponding  acid, 


OH 

OCOOH 
N02 


has  not  been  effected. 


502  ORGANIC  CHEMISTRY.  [§  362 

Groups  occupying  positions  further  separated  sometimes  exert 
a  similar  effect.  One  of  the  NO2-groups  of  symmetrical  trinitro- 
benzene  is  replaced  by  OCH3  through  the  action  of  sodium 
methoxide:  for  trinitrotoluene, 

N02 


NO2 

this  substitution  is  not  found  possible,  the  methyl-group  preventing 
exchange  of  the  nitro-group  even  in  the  para-position. 

Instances  are,  however,  known  of  or^o-substituents  increas- 
ing the  reactivity  of  a  group  situated  between  them. 


HYDROCYCLIC  OR  HYDROAROMATIC  COMPOUNDS. 

363.  A  number  of  compounds  occur  in  nature  containing  pro- 
portions of  hydrogen  intermediate  between  those  in  the  aromatic 
derivatives  with  saturated  side-chains  and  those  in  the  saturated 
aliphatic  derivatives.  These  hydrocyclic  or  hydroaromalic  com- 
pounds are  readily  converted  into  aromatic  bodies.  Caucasian 
petroleum  contains  naphthenes,  with  the  formula  CnH2n,  which 
have  two  hydrogen  atoms  less  than  the  corresponding  saturated 
hydrocarbons,  CnH2n+2,  but  nevertheless  display  all  the  properties 
characteristic  of  saturated  compounds.  The  explanation  is  that 
they  lack  multiple  bonds,  but  have  a  closed  carbon  chain;  thus, 


d/cioHexane 

The  terpenes,  Ci0Hi6,  are  vegetable-products,  and  are  the  prin- 
cipal constituents  of  the  "essential  oils."  These  oils  also  contain 
compounds  of  the  formulae  CioH16O,  CioHxgO,  and  CioH2oO,  among 
them  the  camphors.  Like  the  naphthenes,  the  terpenes  and  cam- 
phors are  readily  converted  into  aromatic  compounds,  and  therefore 
belong  to  the  hydrocyclic  series.  The  progress  recently  made  in 
this  division  of  organic  chemistry  has  rendered  a  systematic  classi- 
fication of  these  compounds  possible. 

Two  principal  methods  are  employed  in  their  preparation: 
by  one  they  are  obtained  from  compounds  of  the  aliphatic  series, 
and  by  the  other  from  those  of  the  aromatic  series.  Several 
examples  of  each  method  will  be  cited. 

On  dry  distillation,  calcium  adipate  yields  c/yfopentanone 
(277).  By  the  same  treatment  calcium  pimelate  is  converted 
into  cyclohexanone: 


PTT      CH2-CH2«CO(X  n         prr     _.CH2  •  CH2 
H2<CH2.CH2.COO>Ca  =     H2<CH2.CH2> 

Calcium  pimelate  cycZoHexanone 

503 


504  ORGANIC  CHEMISTRY.  [§  363 

This  structural  formula  is  established  by  the  ketonic  character  of 
the  compound,  and  by  the  fact  that  dilute  nitric  acid  oxidizes  it 
almost  quantitatively  to  adipic  acid  : 

CH2  •  CH2  •  CO  CH2  •  CH2  •  COOH 

CH2-CH2'CH2  CH2.CH2.COOH* 

cycZoHexanone  Adipic  acid 

Diethyl  succinate  constitutes  an  important  basis  for  the  syn- 
thesis of  other  c^/c/ohexane  derivatives.  In  presence  of  sodium, 
two  molecules  of  it  condense  to  diethyl  succinylsuccinate,  which 
melts  at  127°: 

/COOC2H5  /COOC2H5 

CH2/  CH/ 

I  +  I 

>CH2  yCH2 

C2H5OOC/  C2H5OOC/ 

Diethyl  succinate 

/C0\ 

H2C  CH»COOC'2ri5 

+  2C2H5OH. 
C2H5OOC.HC  CH2 


Diethyl  succinylsuccinate 

The  free  acid,  obtained  by  saponification,  is  decomposed  at  200°, 
with  elimination  of  two  molecules  of  carbon  dioxide,  yielding 
p-diketocyc\ohexane, 


>CH2 CH2v 

C0<  >CO. 

XCH2 CH2/ 


The  structural  formula  of  this  substance  is  indicated  by  this  syn- 
thesis, and  also  by  its  reduction  to  cj/cZohexanone. 

The  second  method  of  obtaining  hydrocyclic  compounds  has 
been  much  simplified  by  the  researches  of  SABATIER  and  SEN- 
DERENS.  They  found  that  many  aromatic  hydrocarbons,  such  as 
benzene  and  its  homologues,  are  readily  hydrogenated  to  hexa- 
methylene  and  its  derivatives  by  passing  their  vapours  mixed  with 


§  364]  HYDROCYCLIC  COMPOUNDS.  505 

hydrogen  over  heated,  finely-divided  nickel,  which  is  obtained  by 
reduction  of  the  oxide,  and  exerts  a  catalytic  influence: 


Benzene  cj/cZoHexane 

Benzoic  acid  can  be  hydrogenated  to  hexahydrobenzolc  acid  by 
the  action  of  sodium  on  its  solution  in  amyl  alcohol  at  the  boiling- 
point.  The  phthalic  acids  and  polybasic  aromatic  acids  are  hydro- 
genated by  treating  them  in  aqueous  solution  with  sodium- 
amalgam. 

In  describing  the  hydrocyclic  compounds,  it  is  convenient  to 
treat  the  cymene  derivatives,  or  terpenes,  separately,  for  they 
exhibit  many  characteristic  properties.  The  other  hydrocyclic 
compounds  will  first  be  briefly  reviewed. 

364.  cvdoHexane  is  the  simplest  member  of  this  group.  It 
is  best  obtained  by  the  method  of  SAB  ATIER"  and  SENDERENS  (363)  . 
Like  its  homologues,  it  is  a  colourless  liquid.  Its  boiling-point,  80°, 
is  very  near  that  of  benzene,  80-4°:  as  the  crude  hydrogenation- 
product  always  contains  benzene,  the  isolation  of  pure  c?/c£ohexane 
from  it  by  fractional  distillation  is  therefore  impracticable.  In 
its  separation,  advantage  is  taken  of  its  stability  at  ordinary  tem- 
peratures towards  fuming  sulphuric  acid  and  concentrated  nitric 
acid,  which  respectively  convert  benzene  into  benzenesulphonic 
acid  and  nitrobenzene.  Since  each  of  these  compounds  is  soluble 
in  the  corresponding  acid,  and  c?/cZohexane  insoluble,  the  sep- 
aration of  the  latter  can  be  readily  effected.  The  melting-point 
(82)  affords  the  best  criterion  of  the  purity  of  c?/cZohexane.  It 
is  6-4°,  and  therefore  approximates  closely  to  that  of  benzene,  5-4°. 

ZELINSKY  has  found  that  at  300°  palladium-black  can  eliminate 
six  hydrogen  atoms  from  q/c/ohexane,  with  formation  of  benzene; 
while  at  100°-110°  this  catalyst  transforms  a  mixture  of  benzene 
and  hydrogen  into  q/cfohexane.  He  has  also  observed  the  remark- 
able fact  that  at  300°  palladium-black  is  incapable  of  abstracting 
hydrogen  from  either  q/dopentane  or  q/c?0heptane.  This  phenomenon 
affords  a  very  valuable  method  of  ascertaining  whether  a  cyclic 
hydrocarbon  is  a  derivative  of  q/cfohexane  or  not,  previously  a  very 
difficult  matter.  The  application  of  this  reaction  is  exemplified  by  a 
hydrocarbon  of  the  formula  C6Hi2,  which  might  be  either  q/c/ohexane, 
(CH2)6,  or  methylq/cZopentane,  (CH2)4>CH-CH«. 


506  ORGANIC  CHEMISTRY.  [§  364 

Chlorine  reacts  very  energetically  with  c?/c£ohexane  in  dif- 
fused sunlight,  and  with  explosive  violence  in  direct  sunlight.  A 
mixture  of  substitution-products  is  formed,  from  which  mono- 
chlorocyclohexane  can  be  obtained  by  fractional  distillation. 
Replacement  of  the  Cl-atom  in  this  compound  by  hydroxyl  is  not 
readily  effected:  treatment  with  alcoholic  potash  converts  it  into 
tetrahydrobenzene,  a  liquid  boiling  at  83°-84°,  and  possessing  all 
the  properties  characteristic  of  unsaturated  compounds. 

When  a  mixture  of  phenol-vapour  and  hydrogen  is  passed  over 
finely-divided  nickel,  cyclohexanol  is  formed.  It  is  a  colourless 
somewhat  thick  liquid  :  it  boils  at  160*  5°,  and  at  a  low  temperature 
solidifies  to  a  camphor-like  mass,  which  melts  at  20°. 

p-Diketocyv\ohexa?ie  (363)  melts  at  78°.  Careful  reduction 
with  sodium-amalgam  in  an  atmosphere  of  carbon  dioxide  converts 
it  into  the  dihydric  alcohol  quinitol: 


y22\  y2»;x 

C0<  >CO  +  4H=HO-CH<  >CH-OH. 

NCH2  •  CH/  XCH2  -  CH/ 

p-DiketocycZohexane  Quinitol 

Two  modifications  of  quinitol  are  known,  distinguished  by  the 
prefixes  cis  and  trans.  They  are  best  prepared  from  quinol  by 
the  reduction-method  of  SABATIER  and  SENDERENS  (363).  They 
can  be  separated  by  means  of  their  acetyl-derivatives.  The 
stereochemical  character  of  their  isomerism  is  indicated  by  a 
consideration  of  Fig.  33  (168),  in  which  a  c?/cZopentyl-rmg  is  repre- 
sented. If  the  pentagon  is  supposed  to  lie  in  the  plane  of  the 
paper,  one  of  the  free  linkings  of  each  carbon  atom  will  lie  above, 
and  the  other  below,  this  plane.  If  a  c?/c£ohexyl-ring  is  simi- 
larly constructed,  there  is  obtained  the  perspective  figure 


in  which  the  affinities  not  forming  part  of  the  ring  are  represented 
by  vertical  lines.  The  isomerism  of  the  quinitols  is  explained,  by 
the  assumption  that  the  hydroxyl-groups  of  the  cis-modification 


§  364]  HYDROCYCLIC  COMPOUNDS.  507 

are  situated  on  the  same,  and  of  the  trans-modification  on  the 
opposite,  side  of  the  hexagon: 


OH 
H 


H 


H         H 
H         H 


H  ,H 


OH  OH 


H  H 


H         H 
H         H 


H 


H 


OH 


H1  IH         Hi 

cia-Quinitol  (M  P.  101°)  <ran*-Quinitol(M  P.  139°) 


Inositol,  C6H12O6,  is  a  hexahydric  alcohol  derived  from  cyclo- 
hexane.  Its  molecular  formula  is  the  same  as  that  of  the  hexoses  : 
on  account  of  its  sweet  taste  and  its  occurrence  in  many  leguminous 
plants,  it  was  formerly  classed  with  the  sugars.  Its  relation  to 
c;yc/ohexane  is  proved  by  its  reduction  with  hydriodic  acid  to 
benzene,  phenol,  and  tri-iodophenol,  and  by  its  conversion  by 
phosphorus  pentachloride  into  quinone  and  substituted  quinones. 
The  presence  of  six  hydroxyl-groups  is  indicated  by  the  formation 
of  a  hexa-acetate.  Inositol  is  also  a  constituent  of  the  heart- 
muscle,  the  liver,  and  the  brain. 

cycloHexanone  can  be  prepared  from  pimelic  acid  (363),  but 
is  more  readily  obtained  by  the  oxidation  of  hexahydrophenol  with 
chromic  acid.  It  boils  at  155°.  Its  alkaline  solution  reacts  with 
benzaldehyde  to  form  a  well-crystallized  condensation-product: 

<H2-CH2x        +OCH-C6H5 
>CO 
H2.CII2/        +OCH-C6H3 

cj/c/oHexanone 


>CO 
C=C 

Dibenzalcj/cZohexanone 

This  reaction  furnishes  a  good  test  for  c?/c/ohexanone. 

The  properties  of  the  hydrocyclic  acids  are  analogous  to  those 
of  the  aliphatic  acids.  Thus,  hexahydrobenzctic  acid  has  a  rancid 
odour,  like  that  of  capric  acid.  It  melts  at  92°,  almost  30°  lower 
than  benzoic  acid,  which  melts  at  121-4°.  The  hydrophthalic 
acids  exhibit  isomerism  which  admits  of  the  same  explanation 
as  that  of  quinitol. 


•;508  ORGANIC  CHEMISTRY.  [§365 


TERPENES. 

365.  The  terpenes  are  hydrogenated  derivatives  of  cymene  and 
its  substitution-products.  Many  of  them  are  vegetable  products. 
They  are  readily  volatile  with  steam,  and  this  property  facilitates 
the  isolation  of  the  natural  terpenes.  The  distillate  separates  into 
two  parts,  an  aqueous  layer  below,  and  a  mixture  of  terpenes  above. 
After  drying,  the  terpene-layer  is  fractionated  several  times  in 
vacuo  to  isolate  its  constituents.  Complete  purification  has  some- 
times to  be  effected  by  conversion  of  the  terpenes  into  derivatives 
which  can  be  freed  from  impurities  by  crystallization:  from  the 
crystalline  compounds  thus  obtained  the  terpenes  can  be  regen- 
erated. 

VON  BAEYER  has  devised  a  rational  nomenclature  for  the 
numerous  derivatives  of  hydrogenated  cymene.  He  numbers  the 
carbon  atoms  of  this  hydrocarbon  as  in  the  scheme 


A  double  linking  between  two  carbon  atoms,  such  as  3  and  4,  is 
denoted  by  J3. 

The  saturated  cyclic  hydrocarbon  hexahydrocymene,  Ci0H2o,  is 
called  menthane.  It  is  not  a  natural  product,  but  can  be  obtained 
by  the  interaction  of  cymene  and  hydrogen  with  nickel  as  a  cata- 
lyst. It  boils  at  168°. 

The  saturated  alcohols  and  ketones  derivable  from  menthane 
are  very  important.  Among  them  is  menthol  or  3-menthanol, 
CioH2oO,  the  principal  constituent  of  oil  of  peppermint,  from  which 
it  crystallizes  on  cooling.  It  forms  colourless  prisms  of  character- 
istic peppermint-like  odour.  It  melts  at  43°. 

Menthol  has  the  constitution 


3661  TERPENES.  509 


CH  . 


H2C        CH2 
H2C        CHOH. 


CH 
CH 

A 

CH3  CH3 

Menthol 

It  is  a  secondary  alcohol,  since  oxidation  with  chromic  acid  elimi- 
nates two  atoms  of  hydrogen,  yielding  a  substance  of  ketonic  charac- 
ter, called  menthone,  a  constituent  of  oil  of  peppermint.  Since  there 
are  several  processes  for  the  conversion  of  menthol  into  cymene  or 
its  derivatives,  it  must  contain  a  cymene-residue.  One  of  these 
methods  also  proves  that  the  hydroxyl-group  is  attached  to  carbon 
atom  3:  when  a  solution  of  menthone  in  chloroform  is  treated  with 
bromine,  there  results  a  dibromomenthone,  from  which  quinoline 
eliminates  2HBr,  forming  thymol  (294), 

CH3 

!OH- 

CH(CH3)2 

Thymol 

When  thymol  is  heated  with  phosphoric  oxide,  it  yields  propyl- 
ene  and  m-cresol  (294),  so  that  its  methyl-group  and  hydroxyl- 
group  must  be  in  the  meta-position. 

366.  Terpin,  C10H18  (OH)  2,  a  clihydric  alcohol,  is  also  a  derivative 
of  menthane.  Its  hydrate,  Ci0H20O2+H2O,  is  obtained  by  keeping 
oil  of  turpentine  in  contact  with  dilute  nitric  acid  and  a  small  pro- 
portion of  alcohol  in  shallow  dishes  for  several  days.  During  the 
process  the  turpentine  takes  up  the  elements  of  three  molecules  of 
water.  Terpin  hydrate  forms  well-defined  crystals,  melting  at  117°. 
On  heating,  it  loses  one  molecule  of  water,  anhydrous  terpin  distil- 
ling at  258°. 

Terpin  can  be  synthesized  from  geraniol, 


510  ORGANIC  CHEMISTRY.  [§  366 

J\C=CH  -CH2  -CH2  .C=CH  -CH2OH. 

Gerauiol 

When  agitated  for  a  prolonged  time  with  sulphuric  acid  of  five  per 
cent,  strength,  geraniol  takes  up  two  molecules  of  water,  being 
almost  quantitatively  converted  into  terpin  hydrate: 
CH3  CH3 

c  C.OH 

H2C          CH  H2C          CH2 

II  II 

H2C          CH2OH  +  2H2O  =  H2C          CH2OH  -  H2O-> 

CH  CH2 

C  C-OH 

/\  /\ 

CH3  CH3  CH3  CH3 

Geraniol  Terpin  hydrate 

CHS 


I.OH 
H2C 
H20          CH2 

\  / 

CH 


C- 


OH 


CH3  CH3 

Terpin 

This  mode  of  synthesis  indicates  that  terpin  is  l:8-dihydroxy- 
menthane,  and  there  is  other  evidence  in  favour  of  this  view. 
Hydriodic  acid  reduces  it  to  menthane,  proving  the  presence  of  a 
cymene-nucleus. 

The  constitutional  formula  indicated  for  terpin  is  confirmed 
by  the  synthesis  of  this  compound  effected  by  W.  PI.  PERKIN^ 
Jun.  Ethyl  sodiocyanoacetate  and  ethyl  ,3-iodopropionate  react 
thus: 


§  366]  TERPENES.  511 

2CN.CHNa-COOC2H5+   2I.CH2.CH2.COOC2H5=2NaI  + 

CNV       /CH2  •  CH2  •  COOC2H5 

+  >C<  +CN.CH2.COOC2H5. 

CaHfiOOCr      XCH2.CH2.COOC2H5 
I. 

Hydrolysis  of  compound  I.  simultaneously  eliminates  carbon 
dioxide  with  formation  of  the  acid 

/CH2.CH2.COOH 
HOOC-CH< 

XCH2.CH2.COOH 

from  which  water  and  carbon  dioxide  are  eliminated  by  heating 
with  acetic  anhydride,  with  formation  of  the  ketonic  acid 

/-ITT     nu 
yUrlo*  Url2v 

HOOC-CH/  ^>CO. 

The  carbethoxyl-group  and  the  carbonyl-group  of  the  ester  of 
this  acid  react  readily  with  methyl  magnesium  iodide  (91  and 
102),  forming  a  compound  of  the  formula 

I 

j 


I-Mg(X  XCH2-CH2 

converted  by  dilute  mineral  acids  into  the  product 


xCri9 


C.CH 


y 


, 

CH2-CH2X     XCH3 


identical  with  terpin. 

Elimination  of  water  from  terpin  yields,  among  other  products 
(367),  a  substance  of  the  formula  CioHlsO,  which  is  neither  an  alco- 
hol nor  a  ketone,  and  is  identical  with  cineol,  a  constituent  of  many 
essential  oils.  Oil  of  eucalyptus  and  oil  of  wormseed  (Oleum 
cince)  contain  a  large  proportion  of  this  compound.  Its  mode 
of  formation  and  properties  indicate  that  cineol  has  the  consti- 
tutional formula 


512  ORGANIC  CHEMISTRY.  [§  367 

CH3 

C 

/XCH 

V^ilo 


TT    r\  /'"'TT 

X12O  ^±12 

C O 

CH^CH 

vJa.3     t^ri3 

Cineol 

367.  Some  of  the  unsaturated  derivatives  of  menthane  are  also 
very  important.  The  menthenes,  C1()H18,  hydrocarbons  with  one 
double  linking  in  their  molecule,  need  not  be  considered,  but  the 
alcohol  terpineol  and  the  ketone  pulegone,  derived  from  them,  merit 
description. 

Terpineol,  CjoH18O,  is  a  constituent  of  some  essential  oils.  It 
has  an  odour  resembling  that  of  lilacs:  it  melts  at  35°,  and  boils  at 
218°.  Terpineol  is  closely  related  to  terpin,  since  agitation  with 
dilute  sulphuric  acid  converts  it  into  terpin  hydrate:  inversely, 
boiling  with  dilute  sulphuric  acid  regenerates  terpineol  from  terpin 
hydrate,  with  elimination  of  water. 

The  constitution  of  terpineol  must  therefore  be  very  similar  to 
that  of  terpin,  the  only  question  being  which  of  the  hydroxyl- 
groups  of  the  latter  has  been  eliminated  from  the  molecule  along 
with  one  hydrogen  atom.  Since  an  optically  active  terpineol  is 
known,  it  must  be  hydroxyl-group  1  of  terpin,  so  that  terpineol  has 
the  constitution  indicated  in  the  scheme 

r\TT  r^TT 

Lol3  V^±13 

I  I 

C  C-OH 


H2C       CH     -» 
H2C       CH2  <- 

Sfi 

i 

H2C       CH2 
M2C       Cxi2 

¥ 

C-OH 

s\ 

C-OH 
vV 

CHs  CH3 

Terpineol 

CH3  CH3 

Terpin 

Carbon  atom  4  in  the  formula  given  is  asymmetric,  whereas  removal 


§  367]  TERPENES.  513 

of  water  from  C-atoms  4:8,  8:9  (  =  8: 10),  or  1:7  could  not  produce 
an  asymmetric  carbon  atom. 

Pulegone,  CioHl6O,  is  the  principal  constituent  of  the  cheap 
oil  of  polei.  It  boils  at  222°,  and  has  a  peppermint-like  odour. 
The  formation  of  an  oxime  indicates  that  it  is  a  ketone.  On 
reduction  with  sodium  and  alcohol,  it  takes  up  four  hydrogen 
atoms,  yielding  menthol,  which  proves  that  the  carbonyl-group  is 
at  position  3: 

CH3  CH3 

CH  CH 

H2C        CH2  H2C 


AD" 


H2C        CO  H2C        CHOH 

Y 


c 

/\  /\ 

r^JT        /^W  f^TT      OTT 

V^XAQ      v^AlL^j  v^-LJ-jj     v^JIii 

Pulegone  Menthol 

Both  oxidation  and  heating  with  water  decompose  pulegone  with 
formation  of  acetone,  so  that  the  double  linking  is  between  C-atoms 
4  and  8. 

Among  the  unsaturated  menthane  derivatives  with  two  double 
linkings  are  the  hydrocarbons  terpinolene,d-limonene,  and  l-limonene, 
and  their  racemic  form,  dipentene.  Each  has  the  formula  Ci0H16. 

Terpinolene  boils  at  185°.  It  is  formed  when  terpineol  is  boiled 
with  oxalic-acid  solution,  one  molecule  of  water  being  eliminated. 
Theoretically,  two  reactions  are  possible: 

CH3  CH3  CH3 

C  C  C 

/\  /\  /\ 

H2C        CH  H2C        CH  H2C        CH 

iH2~H2°  =  H2^      k  "  H2^      AH.' 

CH  C  CH 


C-OH                   c  c 

Hs  CH3  CHs  CH3  CH2  CH3 

Terpineol  Terpinolene  d-  and  I-  Liraonene 

I.                                                   II.  111. 


514  ORGANIC  CHEMISTRY.  [§368 


Since  terpinolene  is  optically  inactive,  and  is  derived  from  the 
cally  active  terpineol,  the  asymmetry  of  the  carbon  atom  must 
have  vanished,  as  in  formula  II.  C-atom  4  of  formula  III.  is  asym- 
metric, as  in  terpineol  itself,  formula  I. 

Formula  III.  is  that  of  the  optically  active  limonene,  which 
occurs  in  many  essential  oils  and  varieties  of  turpentine.  It  has  an 
agreeable,  lemon-like  odour.  Its  constitution  is  inferred  from  two 
facts:  first,  it  is  also  obtained  from  terpineol  by  elimination  of 
water,  effected  by  heating  with  potassium  hydrogen  sulphate; 
second,  addition  of  2HBr  yields  the  same  dibromomenthane  as  is 
obtained  from  terpin  by  exchange  of  the  hydroxyl-groups  for 
bromine: 


CH3 
C-OH 

CH3 
C-Br 

H  C/XCH 

/\ 

H!       5 

Jl2Vy           0x12 

^ni  S2  ^ 

Xl2v^            O-tl-2 

^ 

¥ 

C-OH 

C-Br 

CH3  CH3 

Terpin 

CH3  CH3 

Dibromomenthane 

i 


CH3 

Br 

/\+H 
H2C        CH 

ii2^/  CH2 

\s 

CH 
Br        I 

H+A 


Ltmonene 


Dipentene,  a  constituent  of  oil  of  turpentine,  is  also  obtained 
by  mixing  ^-limonene  and  Z-limonene  in  equal  proportions  by 
weight.  Like  the  limonenes,  it  yields  a  well-crystallized  tetrabro- 
mide,  indicating  the  presence  of  two  double  linldngs  in  its 
molecule.  The  preparation  of  isoprene  from  limonene  is  men- 
tioned in  127. 

368.  Carvone,  OioH140,  is  an  important  ketone  belonging  to 
this  group.  It  is  the  principal  constituent  of  oil  of  carraway,  and 
has  its  characteristic  odour.  It  boils  at  228°.  Related  to  carvone 
is  carvacrol,  which  is  obtained  from  it  by  heating  with  potassium- 
hydroxide  solution: 


3681  TERPENES.  515 

CH3  CH3 

I  C 


HC 
HC 


/\ 


Y 
i, 


C-OH       HC        CO 


CH          HC 


CH2* 


)H 
CHs  CH3  , 

Carvacrol  Carvone 

The  hydroxyl-group  in  carvacrol  is  linked  to  C-atom  2,  since,  on 
heating  with  phosphoric  oxide,  propylene  is  evolved,  and  o-cresbl 
(294)  formed.  The  carbonyl-group  in  carvone  is  assumed,  there- 
fore, to  be  at  position  2.  Carvone  is  proved  to  be  a  ketone  by  the 
formation  of  an  oxime,  called  carvoxime. 

When  nitrosyl  chloride  is  added  to  limonene,  subsequent  elim- 
ination of  HC1  yields  carvoxime : 

/TTT  PTI 

uri3  v^xi-s 

C  C-C1 

H2C        CH  H2C        C:NOH 

+NOC1=  ;    -HC1  = 

HTT    pi  /TT 

2  .Cl2v;  \jtt-2 


LJJV^ 

[2C        C] 


C 


uHa  CHj 


3 

Ldmonene  Limonene  nitroso- 

chloride 

CH3 
C 

HC        C:NOH 

I          I 
-  H2C        CH2 


C 

CH2  CH 

Carvoxime 


516 


ORGANIC   CHEMISTRY. 


[§  369 


This  reaction  proves  that  carvone  contains  one  double  linking 
J8:9,  but  leaves  it  doubtful  whether  the  other  double  linking  is 
JG  or  ji :  7  jn  tne  production  of  terpineol  from  terpin  the  double 
linking  is  formed  between  two  C-atoms  of  the  nucleus,  and  by 
analogy  this  should  also  hold  for  carvone.  Further  evidence  in 
favour  of  the  formula  indicated  is  afforded  by  the  decomposition- 
products  of  the  carvone  molecule,  but  the  details  are  beyond  the 
scope  of  this  work. 

Poly  cyclic  Terpene  Derivatives. 

369.  There  exist  hydrocarbons  of  the  formula  Ci0Hi6  which 
contain  but  one  double  linking,  for  they  take  up  only  two  univalent 
atoms  or  groups.  As  they  contain  four  hydrogen  atoms  less  than 
the  saturated  cyclic  menthane,  CioH20,  they  must  have  a  second 
closed  chain  in  the  molecule.  Moreover,  these  compounds  and 
their  derivatives  are  closely  related  to  cymene,  most  of  them  being 
convertible  into  it  or  kindred  substances.  Investigation  has  shown, 
that  the  formation  of  the  second  ring  can  take  place  in  three  different 
ways,  as  the  formulae  indicate: 

CH3  CH3 

CH  CH 

'\ 

H2C 


CH 

Camphane 


369] 


TERPENES. 


517 


The  tertiary  carbon  atom  takes  part  in  the  formation  of  the 
ring,  or  "bridge-formation."  Carane  has  a  trimethylene-ring, 
pinane  a  tetramethylene-ring,  and  camphane  a  pentamethylene- 
ring.  Several  members  of  these  three  groups  will  be  considered. 

Carane  itself  is  unknown,  but  there  is  a  synthetic  derivative, 
carone,  which  is  not  a  natural  product.  It  has  the  structural 
formula 

CH3 

CH 
H2C        CO 


H2C        CH 

VL\ 


CH 


Carone 


for  opening  of  the  trimethylene-ring  at  3 : 8  yields  derivatives  of 
p-cymene,  and  at  4:8  derivatives  of  m-cymene. 

Pinene  is  the  typical  member  of  the  pinane-group.  It  is  the 
principal  constituent  of  the  various  oils  of  turpentine,  and  is, 
therefore,  also  of  technical  importance.  It  is  optically  active,  a 
dextro-rotatory,  a  laevo-rotatory,  and  an  inactive  modification  being 
known.  It  boils  at  156°.  The  presence  of  a  double  bond  is  proved 
by  addition  of  one  molecule  of  hydrochloric  acid,  the  dry  gas  pre- 
cipitating from  cooled  oil  of  turpentine  a  compound  of  the  formula 
CioH16-HCl,  called  "artificial  camphor,"  which  resembles  camphor 
both  in  appearance  and  odour.  Pinene  also  readily  forms  an  addi- 
tion-product with  nitrosyl  chloride.  Pinene  has  the  formula 

CH3 

C 


518  ORGANIC  CHEMISTRY.  [§  370 

The  presence  of  a  tetramethylene-ring  is  assumed  in  order  to  ex- 
plain the  constitution  of  oxidation-products  of  pinene,  such  as 
pinonic  acid  and  pinic  acid,  and  for  other  reasons.  Under  the 
influence  of  benzenesulphonic  acid,  pinene  in  acetic-acid  solution 
combines  with  one  molecule  of  water  to  form  terpineol,  the 
tetramethylene-ring  being  opened.  This  transformation  indi- 
cates the  position  of  the  double  bond. 

CAMPHORS. 

370.  Ordinary  camphor,  CioHieO,  is  the  most  important  mem- 
ber of  the  camphane-group.  No  other  organic  compound  has  been 
so  much  investigated,  or  from  such  widely  different  points  of 
view.  Ordinary,  dextro-rotatory,  "Japan  camphor  "  is  obtained 
by  the  steam-distillation  of  the  bark  of  the  camphor-tree.  It 
forms  a  white,  soft,  crystalline  mass  of  characteristic  odour,  and 
sublimes  even  at  the  ordinary  temperature.  It  melts  at  175*  7°, 
and  boils  at  209.1°. 

The  camphor-odour  is  characteristic  of  many  compounds  theo- 
retically derived  by  substitution  of  all  the  hydrogen  atoms  attached 
to  a  single  carbon  atom ;  that  is,  of  tertiary  compounds.  Very  few 
of  the  relations  between  odour  and  chemical  constitution  have  been 
discovered,  but  many  compounds  containing  a  double  bond  are 
characterized  by  their  pleasant  aroma,  while  that  of  substances  with 
a  triple  bond  is  frequently  disagreeable. 

Camphor  is  a  saturated  ketone — saturated  because  it  does  not 
yield  addition-products,  and  a  ketone  because  it  forms  an  oxime. 
Reduction  converts  it  into  a  secondary  alcohol,  borneol  or  "  Borneo 
camphor  ": 

C9H16.CO+2H  =  C»H16-CHOH. 

Camphor  Borneol 

In  addition  to  the  car  bony  1-group,  the  camphor  molecule  con- 
tains a  methylene-group,  for  it  has  the  properties  of  compounds 
with  the  group — CH2-CO — .  As  explained  in  199,  the  hydrogen 
of  such  a  methylene-group  can  be  replaced  by  the  oxime-group  by 
the  action  of  amyl  nitrite  and  hydrochloric  acid.  Camphor  reacts 
similarly,  these  reagents  converting  it  into  isonitrosocamphor, 
which  melts  at  153°: 


370]  CAMPHORS.  519 


C8H14|       _>C8H14 


/CH2  /C=NOH 

<| 

x^o 

Camphor  isoNitrosocamphor 

Elimination  of  the  oxime-group  from  isonitrosocamphor  yields 
camphor-quinone, 

/CO 

<;i  . 

XJO 

On  treatment  with  hydrogen  peroxide,  this  compound  is  oxidized, 
forming  the  anhydride  of  camphoric  acid, 

COOH 


which  can  also  be  obtained  directly  from  camphor  by  oxidation 
with  nitric  acid.  It  follows  that,  given  the  constitution  of  cam- 
phoric acid,  that  of  camphor  can  be  inferred. 

Ordinary  camphoric  acid  is  dextro-rotatory,  and  melts  at  187°. 
Four  optically  active  camphoric  acids  are  known:  dextro-rotatory 
and  laBvo-rotatory  camphoric  acid,  and  dextro-rotatory  and  laBvo- 
rotatory  isocamphoric  acid,  with  the  same  constitution  as  camphoric 
acid.  These  facts  indicate  that  the  molecule  of  camphoric  acid 
must  contain  two  dissimilar  asymmetric  C-atoms  (188)  . 

Energetic  oxidation  converts  camphoric  acid  into  the  tribasic, 
optically  active  camphoronic  acid,  the  constitution  of  which  follows 
from  its  synthesis,  and  from  its  decomposition-products  when  sub- 
mitted to  dry  distillation.  This  process  decomposes  it  into  tri- 
methylsuccinic  acid,  isobutyric  acid,  carbon  dioxide,  and  carbon: 

(CH3)2C  •  COOH  (CH3)2C  •  COOH 

CH3-C-COOH       =     CHs-CH-COOH-H 
CH2-COOH       +C+H2+CO2 

Camphoronic  acid 

and 

(CH3)2CH.COOH  + 


+C02. 


520  ORGANIC  CHEMISTRY.  [§  370 

From  these  facts  it  is  possible  to  deduce  a  formula  for  camphoric 
acid,  which  also  accounts  for  its  other  properties: 

COOH        COOH  CH2 CH COOH 

I 


GH3 G GH 


CH3— C— CH3 


CH2  --  C—     —COOH        CH2—     —C  ---  COOH 


H3 

Camphoronic  acid 

GH2 


This  structural  formula  for  camphor  was  originally  proposed  by 
BREDT.  His  view  has  been  confirmed  by  the  synthesis  of  camphor, 
effected  by  W.  H.  PERKIN,  JUN.,  and  THORPE,  and  by  KOMPPA, 
but  the  details  of  the  processes  involved  are  beyond  the  scope  of 
this  work.  The  formula  of  camphor  contains  two  dissimilar, 
asymmetric  C-atoms,  represented  in  italic. 

The  position  of  the  carbonyl-group  in  camphor  follows  from  its 
conversion  into  carvacrol  by  the  action  of  iodine :  in  this  compound 
the  hydroxyl-group  is  in  the  ortho-position  to  the  methyl-group 

(368). 

Borneol  contains  a  CHOH-group  instead  of  the  CO-group  present 
in  camphor.     By  replacement  of  the  hydroxyl-group  by  iodine,  it 
yields  bornyl  iodide,  which  can  be  reduced  to  camphane: 
CH2 GH CH2 


According  to  the  formula,  the  conversion  of  CO  into  CH2  should 
destroy  the  asymmetry  of  both  the  asymmetric  C-atoms  of  camphor, 
and  camphane  is,  in  fact,  optically  inactive. 


§  370]  CAMPHORS.  521 

The  formula  of  camphor  contains  an  zsopropyl-group  and  there- 
fore accounts  for  the  conversion  of  camphor  into  cymene  by  heat- 
ing with  phosphorus  pentasulphide.  The  complete  syntheses  of 
camphoric  acid  previously  mentioned  have  definitely  settled  the 
constitution  of  this  acid,  and  that  of  camphor  itself. 

In  the  chemistry  of  the  terpenes  and  camphors  molecular  refrac- 
tion has  been  an  important  aid  in  confirming  structural  formulae 
based  on  purely  chemical  methods,  and  also  in  indicating  the  correct 
formulae  in  cases  to  which  chemical  processes  are  inapplicable. 
Among  the  principles  underlying  the  refraction  method,  two  have 
been  very  useful  in  these  investigations:  (a)  a  double  carbon  linking 
increases  the  molecular  refraction;  (6)  the  formation  of  a  ring  has  no 
influence  on  the  molecular  refraction,  except  that  the  production  of 
a  trimethylene-ring  causes  an  exaltation  of  the  constant,  although 
less  than  that  due  to  a  double  bond. 

Examples. — 1.  The  molecular  refraction  determined  for  camphor 
is  identical  with  that  calculated,  proving  the  absence  of  double 
carbon  bonds  from  the  camphor  molecule. 

2.  A  camphor  derivative,  thujone  or  tanacetone,  CioHuO,  has  the 
molecular  refraction  ffiD  =44«78;  while  that  calculated  for  a  saturated 
ketone  Ci0Hi60  is  44 •  11 ;  and  for  a  kctone  Ci0HiG0  with  one  double 
carbon  bond  45  •  82.  The  fact  of  the  observed  molecular  refraction 
being  intermediate  between  these  two  values  indicates  the  presence 
of  a  trimethylene-ring. 

POLYTERPENES. 

The  polyterpenes  include  a  number  of  compounds  of  the  for- 
mula (C5H8)n,  n  being  greater  than  2. 

The  most  important  member  of  the*  class  is  caoutchouc  or 
india-rubber,  the  latex  or  coagulated  milky  juice  of  various  tropical 
plants,  chief  among  them  Hevea  brasiliensis.  Caoutchouc  is 
purified  by  dissolving  it  in  chloroform  or  another  solvent,  and 
precipitating  it  with  alcohol  in  a  white,  amorphous  form.  It  is 
vulcanized  by  the  action  of  sulphur  or  sulphur  monochloride, 
S2C12,  a  process  considerably  augumenting  its  elasticity  and 
durability.  Un vulcanized  caoutchouc  becomes  sticky  at  30°, 
and  loses  its  elasticity  at  0°.  Over-vulcanization  yields  ebonite 
or  vulcanite. 

The  constitution  of  caoutchouc  has  in  great  measure  been 
elucidated  by  HARRIES.  He  passed  ozone  through  its  solution 


522  ORGANIC  CHEMISTRY.  [§  370 

in  chloroform,  and  obtained  a  vitreous  mass  of  the  formula 
CioHioOe,  which  proved  to  be  a  diozonide,  thus  demonstrating 
the  presence  of  two  double  bonds  in  the  molecule  of  caoutchouc. 
This  diozonide  is  converted  quantitatively  by  water  into  Icevulal- 
dehyde  and  laevulaldehyde  peroxide.  On  the  basis  of  these  facts, 
the  structure  of  the  hydrocarbon  corresponding  with  this  ozonide 
must  be  assumed  to  involve  a  ring  of  eight  atoms  with  two  double 
bonds  : 

CH3  CH3 

C  Og-C  CH3  CHO 


HC      CH2  HC       CH2  OC  CH2 

II                       I         I         H20         I  I 

H2C      CH2  >  H2C       CH2 *    CH2      +     CH2  . 

II  II  I  I/O 

H2C      CH  H2C       CH  CH2  C<   I 

V  \/l  I  |X> 

C  C-O3  CHO  CH3 

CH3  CH3 

!:5-Dimethylc2/cZo-  Diozonide  Laevulaldehyde  Peroxide 

octadiene 

Caoutchouc  is  a  polymeride  of  l:5-dimethylcyc\ooctadiene. 

Tht  great  technical  importance  of  this  substance  has  led  to 
many  attempts  to  prepare  it  synthetically,  finally  effected  by 
the  polymerization  of  isoprene,  C5Hg  (127).  No  method  for 
manufacturing  this  hydrocarbon  on  a  commercial  basis  has 
hitherto  been  devised. 


BENZENE-NUCLEI  LINKED  TOGETHER  DIRECTLY,  OR 
INDIRECTLY  BY  CARBON. 

371.  The  simplest  possible  compound  of  this  nature  is  one  con- 
taining two  benzene-nuclei  directly  linked  together.  In  addition, 
there  are  compounds  with  the  benzene-nuclei  indirectly  connected 
by  a  carbon  atom,  or  by  a  chain  of  carbon  atoms.  A  few  typical 
examples  will  be  cited. 

Diphenyl,  C6H5.C6H6. 

Diphenyl  can  be  best  prepared  by  heating  iodobenzene  with 
finely-divided  copper  at  220°.  Another  method  for  the  preparation 
of  the  derivatives  of  diphenyl,  the  con  version  of  hydrazobenzeneinto 
benzidine,  is  mentioned  in  301.  On  removal  of  the  amino-groups 
from  benzidine  by  means  of  the  diazo-reaction,  diphenyl  remains. 
This  method  of  formation  also  affords  a  proof  of  the  constitution 
of  benzidine. 

Oxidation  converts  diphenyl  into  benzoi'c  acid.  This  reaction 
and  its  synthesis  prove  its  constitution. 

Diphenyl  forms  large,  tabular,  colourless  crystals,  readily  soluble 
in  alcohol  and  ether.  It  melts  at  71°,  and  boils  at  254°. 

The  isomeric  substitution-products  of  diphenyl  are  much  more 
numerous  than  those  of  benzene,  as  the  scheme  indicates: 


Diphenyl 

A  monosubstitut ion-product  can  exist  in  three  isomeric  forms,  the 
substituent  being  in  the  or^/io-position,  mda-position,  or  para-posi- 
tion to  the  bond  between  the  benzene-nuclei.  In  a  disubstitution- 

523 


524  ORGANIC    CHEMISTRY.  §372] 

product,  both  substituents  may  be  linked  to  the  same  benzene- 
nucleus,  or  to  different  benzene-nuclei,  and  so  on. 

Benzidine  is  of  technical  importance,  because  many  of  the  azo- 
dyes  are  derived  from  it. 


Diphenylmethane,  C6H5.CH2-C6H5. 

372.  Diphenylmethane  can  be  obtained  from  benzyl  chloride, 
H^Cl,  or  from  methylene  chloride,  CH2C12,  by  means  of 
benzene  and  aluminium  chloride.  Its  homologues  are  obtained  by 
the  action  of  benzene  and  concentrated  sulphuric  acid  upon  alde- 
hydes. Thus,  acetaldehyde  yields  unsymmetrical  diphenylethane: 


When  derivatives  of  benzene  are  substituted  for  benzene  itself, 
many  derivatives  of  diphenylmethane  can  be  obtained  by  the 
application  of  these  syntheses. 

Diphenylmethane  is  crystalline.  It  melts  at  26°,  boils  at  262°, 
and  has  an  odour  resembling  that  of  orange-peel.  Oxidation  with 
chromic  acid  converts  into  benzophenone  (316). 

A  derivative  of  diphenylmethane,  in  which  the  benzene-nuclei 

C,H4\ 
are  directly  linked,  isfluorene,   \        /CH2.     It  is  formed  by  leading 

CaH/ 

the  vapour  of  diphenylmethane  through  a  red-hot  tube.  From 
alcohol  it  crystallizes  in  leaflets:  the  rrystals  are  fluorescent,  a  cir- 
cumstance which  gave  this  compound  its  name.  It  melts  at  113°, 
and  boils  at  295°.  It  yields  red  needles  with  picric  acid. 

The  constitution  of  fluorene  is  thus  established.     It  is  converted 
by  the  action  of  oxidizing  agents  into  diphenyleneketone,  the  formula 

CeH4x 
of  which,   |         /CO,  is  established  by  its  formation  when  the  cal- 


>Ca,  is  distilled.     Diphenic 


cium  salt  of  diphenic  acid,    \ 


C6H4 


COO' 


acid,  for  its  part,  is  obtained  from  m-hydrazobenzoi'c  acid  by  the 


373]  FLUORENE  AND   TRIPHENYLMETHANE.  525 

benzidine-transformation  (301),  and  subsequent  elimination  of  the 
amino-groups: 


NH-NH    O      -*  HN2  -  NH 


12' 


I  I 

COOH  HOOC 

It  follows  that  the  carbonyl-group  in  diphenyleneketone  is  linked  at 
the  ortho-position  in  both  the  benzene-nuclei :  it  has,  therefore,  the 
structure 


CH2 

This  view  receives  confirmation  from  the  fact  that  phthalic  acid  is 
the  only  product  obtained  by  its  oxidation. 

The  hydrogen  e>f  the  CH2-group  in  fluorene  can  be  replaced  by 
potassium.  Oxidation  of  fluorene  with  lead  oxide  at  310°-330° 
yields  di-diphenylene-ethylene, 


which  melts  at  188°.     It  is  characterized  by  its  deep-red  colour, 
most  hydrocarbons  being  colourless,  at  least  in  thin  layers  (288). 

Triphenylmethane  and  its  Derivatives. 

373-  Triphenylmethane,  CH(C6H5)3,  is  formed  from  benzal  chlor- 
ide, C6H5-CHC12,  by  the  action  of  benzene  and  aluminium  chloride; 
from  benzaldehyde  and  benzene  in  presence  of  a  dehydrating  agent, 
such  as  zinc  chloride;  and  from  the  interaction  of  chloroform  and 
benzene  in  presence  of  aluminium  chloride.  It  crystallizes  in  beau- 
tiful, colourless  prisms  melting  at  93°.  Its  boiling-point  is  359°. 

A  series  of  important  dyes,  the  rosanilines,  is  derived  from  this 
hydrocarbon.  Triphenylmethane  itself  is  not  employed  as  a  basis 
for  their  preparation,  but  simpler  substances  which  are  converted 
into  its  derivatives.  The  formation  of  the  dye  takes  place  in  three 
stages :  malachite-green  furnishes  an  example. 


526  ORGANIC  CHEMISTRY.  [§  373. 

When  benzaldehyde  and  dimethyl  aniline  are  heated  with  zinc 
chloride,  tetramethyldiaminotriphenylmethane  is  formed : 


N(CH3)2  /C6H4N(CH3)2 

=  H20+C6H5.C< 
/N(CH3)2  XC6H4N(CH3)2 


The  carbon  atom  of  the  aldehyde  group,  therefore,  furnishes  the 
"methane  carbon  atom  "  of  triphenylmethane. 

This  substance  is  also  called  leucomalachite-green.     It  is  con- 
verted by  oxidation  with  PbO2,  in  hydrochloric-acid  solution,  into 

C6H5C[C6H4N(CH3)2]2 

the   corresponding   carbmol,  •  ,  a   colourless, 

OH 

crystalline  substance,  like  the  leuco-compound  from  which  it  is 
derived.  Being  an  amino-base,  it  is  capable  of  yielding  salts:  thus, 
it  dissolves  in  acids  with  the  formation  of  colourless  salts.  When 
such  a  solution  is  warmed,  water  is  eliminated,  and  the  deep-green 
dye  produced.  The  dye,  either  as  a  double  salt  with  zinc  chloride, 
or  as  an  oxalate,  is  known  as  malachite-green.  The  elimination  of 
water  may  be  represented  in  several  ways;  it  is  usually  supposed 
to  take  place  thus : 

/CeH^CH^.HCl 

-H20« 

4.N(CH3)2.[HlCl 


|OH| 

5H4N(CH3)2.HC1 
>=N(CH3)2. 
Cl 

Quinonoid  form 

This  "quinonoid  reaction  "  is  analogous  to  the  formation  of  quinone 
from  quinol,  in  which  the  colourless  quinol  is  converted  into  the 
deep-yellow  quinone. 

The  conversion  into  a  quinonoid  form  also  explains  many  other 
instances  of  the  formation  of  coloured  substances;  for  example,  the 


§373]  QUINONOID    STRUCTURE.  527 

conversion  of  the  colourless  phenolphthaleiin  (348)  into  its  red  metal- 
lic derivative. 

BERNTHSEN  has  proved  that   this   indicator   in   the  colourless 

state  is  a  lactone, 

C(C6H4OH)2 


CO 

but  that  its  red  salts  are  derivatives  of  a  carboxylic  acid  containing 
a  quinonoid-group, 

XC6H4:0 
C\ 

NC6H4OH 


I 


COO 


Me* 


When  the  phenolphthalei'n  is  regenerated  from  this  salt  by  the  action 
of  an  acid,  it  changes,  like  the  pseudo-acids  (322),  into  the  colour- 
less lactone-fonn,  the  transformation  in  this  case  being  instantaneous. 

The  distinguishing  characteristic  of  the  group  >C6H4<  is  its 
strongly  marked  chromophore  character. 

The  nitrophenols  constitute  one  of  the  many  examples  of  this 
phenomenon.  In  the  pure  state  both  they  and  their  ethers  are 
quite  colourless,  but  their  salts  are  highly  coloured.  It  has,  however 
been  possible  to  prepare  highly  coloured  ethers  of  the  nitrophenols, 
and  by  various  reactions  to  transform  them  into  colourless  ethers 
with  the  same  molecular  weight.  The  isomerism  of  these  compounds 
is  explicable  on  the  assumption  for  the  colourless  derivatives  of  the 

/NO, 

normal  structure  C6H4\        ,  and  for  the  coloured  products  of  the 
\)R 

NO  -OR 
quinonoid  structure  C6H4|f  ,  the  nitrophenols  being  regarded 


as  pseudo-acids  with  a  quinonoid  aci-form. 

VON  BAEYER  has  pointed  out  that  the  development  of  colour 
is  not  always  due  to  transformation  into  a  quinonoid  form.  The 
intensely  coloured  acid  salts  of  trianisijlcarbinol,  (CHsO'CeH^aOOH, 
and  of  similar  compounds  undoubtedly  are  not  quinonoids.  Their 
colour  is  probably  caused  by  intramolecular  rearrangement  of  an  ob- 
scure type.  VON  BAEYER  has  named  this  phenomenon  halochromy. 

*  Me  represents  one  equivalent  of  a  metal. 


528  ORGANIC  CHEMISTRY.  [§  374 

374.  The  three  stages  necessary  to  the  formation  of  the  dye, 
may,  therefore,  be  defined  as  follows. 

1.  Formation    of    a    leuco-base  (colourless),    a    derivative  of 

HC(C6H4NH2)3, 

2.  Formation  of  a  colour-base  (colourless),  a  derivative  of 

HO.C(C6H4NH2)3. 

3.  Formation  of  the  dye,  a  derivative  of 

p(C6H4NH2,HCl)2 
UC6H4NH2.C1 

Reduction   reconverts   the   dyes  into  their  leuco-bases,   two 
hydrogen  atoms  being  taken  up  during  the  reaction. 

Crystal-violet  (hexamethyltriaminotriphenylmethane)  furnishes  an 
excellent  example  of  a  phenomenon  also  exhibited  by  other  ana- 
logous basic  substances.  When  an  equivalent  quantity  of  an  alkali 
is  added  to  a  salt  of  crystal-violet,  the  liquid  still  remains  coloured, 
has  a  strong  alkaline  reaction,  and  conducts  an  electric  current. 
On  standing,  the  solution  slowly  becomes  colourless,  when  it  is  no 
longer  alkaline,  and  its  electric  conductivity  has  fallen  to  that  of 
the  alkali-metal  salt  present  in  the  liquid.  The  liquid  now  contains 
a  colour-base.  These  phenomena  are  analogous  to  the  conversion  of 
acids  into  pseudo-acids  (322).  For  this  reason  the  colour-base  may 
be  looked  upon  as  a  pseudo-base.  Thus,  on  addition  of  the  equiva- 
lent quantity  of  NaOH  to  crystal-violet,  the  true  base, 

(CH3)2N  •  C0H4 .   r_/=\_N  (CH3)2 
(CH3)2N.C6H4>    ~\^/—NOH 

is  at  first  present  in  the  solution:  after  standing  for  several  hours  at 
25°,  however,  this  true  base  changes  into  the  colour-base  (pseudo- 
base), 

(CH3)2N  -  C6H4     p    C6H4  •  N  (CHS)2. 

(CH3)2N.C6H4>     <OH 

HANTZSCH  has  been  able  to  identify  as  pseudo-bases  substances 
other  than  those  mentioned. 


§  374]  TRIPHENYLMETHANE  DYES.  529 

Pararosaniline  is  obtained  by  the  oxidation  of  a  mixture 
of  p-toluidine  (1  molecule)  and  aniline  (2  molecules)  by  me^ans  of 
arsenic  acid  or  nitrobenzene.  The  methyl-group  of  toluidine  thus 
furnishes  the  "  methane  carbon  atom"  of  triphenylmethane: 

/C6H4.NH2  /C6H4NH2 

CH/  C6H5.NH2+3O  =  HO—  C^C6H4NH2  +  2H2O. 
C6H5.NH2  \C6H4NH2 

This  colour-base  dissolves  in  acids,  forming  a  red  dye:  it  can  be 
reprecipitated  by  alkalis.  It  is  transformed  by  reduction  with  zinc- 
dust  and  hydrochloric  acid  into  paraleucaniline  ,  HC(C6H4NH2)3? 
a  colourless,  crystalline  substance  which  melts  at  148°,  and  is  recon- 
verted into  the  colour-base  by  oxidation.  The  constitution  of 
paraleucaniline  is  indicated  by  the  formation  of  triphenylmethane 
on  elimination  of  its  ammo-groups  by  diazotization.  On  the 
other  hand,  paraleucaniline  can  be  obtained  by  the  nitration  of 
triphenylmethane,  and  subsequent  reduction  of  the  trinitro- 
derivative  thus  formed.  Paraleucaniline  is  converted  by  oxidation 
into  triaminotriphenylcarbinol,  which,  like  malachite-green,  loses 
water  under  the  influence  of  acids,  forming  the  dye: 

/C6H4NH2  /C6H4NH2 

C^-C6H4NH2         -H2O  =  C^C6H4NH2 
|  \C6H4NH2  .  HC1  X^H4  :  NH2  .  Cl. 

OH 

Another  important  dye  related  to  triphenylmethane  isrosaniline.- 
Its  preparation  is  similarly  effected  by  oxidizing  a  mixture  of  ani- 
line, o-toluidine,  and  p-toluidine  in  equimolecular  proportions  with 
arsenic  acid,  mercuric  nitrate,  or  nitrobenzene.  In  this  reaction  the 
methane  carbon  atom  is  obtained  from  p-toluidine  as  follows: 

NH2  .  C6H4  •  CH3  +  C6H4(CH3)NH2  +  C6H5  .  NH2    + 

p-Toluidine  o-Toluidine 

P     TT      ^ 

UH3  < 


C6H4NH2  C6H4  :  NH2  .  CL 

Colour-base  Magenta 

The   chloride   obtained   from   the   rosaniline   colour-base,   by 
combination  with  one  equivalent  of  hydrochloric  acid  and  elimina- 


530  ORGANIC  CHEMISTRY.  [§  374 

tion  of  one  molecule  of  water,  is  called  magenta.  This  substance 
forms  beautiful  green  crystals  with  a  metallic  lustre,  which  dis- 
solve in  water,  yielding  a  solution  of  an  intense  deep-red  colour. 
The  colour  of  the  magenta  solution  is  due  to  the  univalent 
cation,  (CooH^oNs),  because  such  solutions  are  almost  completely 
ionized,  as  the  slight  increase  of  their  molecular  conductivity  on 
further  dilution  shows.  Moreover,  the  solutions  of  all  the 
magenta  salts — chloride,  bromide,  sulphate,  etc. — exhibit  the 
same  absorption-spectrum  for  solutions  of  equimolecular  con- 
centration, an  indication  of  the  presence  of  .a  constituent  common 
to  all  of  them  (the  cation). 

The  salts  containing  three  equivalents  of  acid  are  yellow,  the  red, 
univalent  cation  having  been  converted  into  the  yellow,  tervalent 
cation:  in  consequence,  magenta  dissolved  in  excess  of  hydrochloric 
acid  yields  a  nearly  colourless  solution.  These  salts  are,  however, 
very  readily  hydrolyzed :  the  red  colour  reappears  when  this  solution 
in  hydrochloric  acid  is  poured  into  water.' 

Many  derivatives  of  pararosaniline  and  rosaniline  are  known  in 
which  the  hydrogen  atoms  of  the  amino-group  have  been  replaced 
by  alkyl-radicals.  They  are  all  dyes.  The  violet  colour  becomes 
deeper  as  the  number  of  methyl-groups  present  increases  (341). 
Pentamethylpararosaniline  has  the  trade-name  "methyl-violet." 
When  one  hydrogen  atom  in  each  of  the  amino-groups  of  rosaniline 
is  replaced  by  phenyl,  a  blue  dye  is  formed,  called  "aniline-blue." 

Methyl- violet  is  obtained  by  the  oxidation  of  dimethylaniline  with 
potassium  chlorate  and  cupric  chloride,  the  methane  carbon  atom 
being  obtained  from  one  of  the  methyl-groups. 

Aniline-blue,  or  triphenylrosaniline  hydrochloride,  is  formed  by  heat- 
ing rosaniline  with  aniline  and  a  weak  acid,  such  as  benzole  acid, 
whereby  the  amino-groups  in  the  rosaniline  are  replaced  by  anilino- 
groups,  the  ammonia  set  free  entering  into  combination  with  the 
acid.  This  process  in  analogous  to  the  formation  of  diphenylamine 
from  aniline  hydrochloride  and  aniline  (298). 

Dyes  formed  from  hydroxyl-derivatives  of  triphenylmethane 
are  also  known,  but  are  much  less  valuable  than  those  just 
described,  on  account  of  the  difficulty  of  fixing  them.  Rosolic 
acid, 


375]  TRIPHENYLMETHYL.  531 

3 


obtained  from  rosaniline  by  diazotization,  is  an  example  of  such 
dyes. 

Malachite-green  and  the  pararosaniline  and  rosaniline  dyes 
colour  wool  and  silk  directly,  and  calico  after  it  has  been  mordanted. 

It  is  stated  in  340  that  the  fixing  of  dyes  upon  vegetable  or 
animal  fibres,  must  be  regarded  as  a  chemical  combination  of  the 
compounds  contained  in  the  fibre  with  the  dye,  analogous  to  the 
formation  of  salts.  The  following  is  a  proof.  The  colour-base  of 
rosaniline  is  colourless:  when,  however,  wool  or  silk  is  immersed 
in  its  colourless  solution,  it  becomes  gradually  coloured,  as  though 
an  acid  had  been  added.  This  phenomenon  can  only  be  explained 
by  supposing  that  a  compound  in  the  fibre  unites  with  the  colourless 
base,  forming  with  it  a  salt  of  the  same  colour  as  a  solution  of  the 
dye  in  water. 

The  phthalems,  dyes  related  to  triphenylmethane,  have  been 
mentioned  (348). 

375.  GOMBERG  has  investigated  the  action  of  zinc  upon  a 
benzene  solution  of  triphenylchloromethane  :  zinc  chloride  separates 
and  the  solution  contains  a  compound  which  can  be  precipitated 
by  addition  of  acetone  or  ethyl  formate.  This  compound  ho 
regards  as  triphenylmethyl,  (CeH^aC  —  ,  with  one  free^linking.  Its 
power  of  forming  addition-products  is  remarkable.  It  is  at  once 
oxidized  by  atmospheric  oxygen  to  a  peroxide, 

(C6H5)3C—  O—  O—  C(C6H5)3. 

It  decolorizes  iodine-solution  instantaneously,  forming  triphenyl- 
methyl iodide.  It  yields  addition-products  with  ether  and  many 
other  compounds. 

A  close  investigation  of  triphenylmethyl  has  revealed  the 
existence  of  two  forms,  one  being  colourless  and  the  other  yellow. 
The  solid,  colourless  hydrocarbon  is  converted  by  solution  into 
the  yellow  isomeride,  the  only  highly  reactive  form.  In  solu- 
tion, the  two  modifications  attain  an  equilibrium  dependent  on, 
the  temperature  and  the  nature  of  the  solvent.  Since  the  mo- 
lecular weight  indicated  by  the  cryoscopic  method  corresponds 
with  nearly  twice  the  empirical  formula,  the  equilibrium 


532  ORGANIC  CHEMISTRY.  [§376 


<=>   (C6H5)3C.C(C6H5)3 

Triphenylmethyl  Hexaphenylethane 

requires  the  presence  of  only  a  small  percentage  of  the  yellow 
modification. 

The  colourless  form  consists  of  hexaphenylethane  ,  and  the 
yellow  isomeride  of  triphenyl  methyl.  In  tridiphenylmethyl  , 
(CeHs'CeH^C,  the  unimolecular  form  predominates  strongly, 
the  solution  having  an  intense  violet  colour.  These  compounds 
recall  the  parallel  instance  of  nitrogen  peroxide,  known  in  a 
colourless  form,  N2O4,  and  in  a  yellowish-brown  modification, 
NO2.  Like  triphenylmethyl,  the  simpler  form  of  nitrogen  per- 
oxide is  characterized  by  its  abnormal  condition  of  unsaturation. 

In  two  respects  these  compounds  are  very  remarkable:  first, 
triphenylmethyl  contains  a  tervalent  carbon  atom;  second,  the 
carbon  linking  in  hexaphenylethane  can  be  severed  with  extraor- 
dinary ease,  even  by  mere  solution  in  benzene  or  other  solvents. 
Among  the  reasons  for  assuming  the  colourless  compound  to  be 
hexaphenylethane  is  its  analogy  to  pentaphenylethane,  a  sub- 
stance readily  decomposed  at  high  temperature,  but  proved  by 
its  synthesis  to  have  the  structure  (Cells)  3C 


Dibenzyl  and  its  Derivatives. 

376.  Dibenzyl,  C6H5«CH2'CH2-CeHs,  can  be  obtained  by  the 
action  of  sodium  upon  benzyl  chloride: 


C6H5.CH2|Cl+Na2+Cl|CH2.C6H5  =  C6H5.CH2.CH2.C6H5+2NaCl. 

This  method  of  formation  shows  it  to  be  symmetrical  diphenyl* 
ethane.     It  melts  at  52°. 

Symmetrical  diphenylethylene,  C6H5-CH:CH-C6H5,  M.P.  125°,  is 
called  stilbene.  It  can  be  obtained  by  various  methods :  for  example, 
by  heating  an  aqueous  solution  of  phenylsodionitromethane,  which 
is  thereby  decomposed  into  stilbene  and  sodium  nitrite : 

2C6H5.CH:NO-ONa  =  C6H5.CH:CH.C0H5+2NaNO2. 

Stilbene  forms  an  addition-product  with  bromine,  from  which 
tolan,  CttH5'C  =C'C(iH5,  is  produced  by  elimination  of  2HBr.  Tolan 
can  be  reconverted  into  stilbene  by  careful  reduction. 

p-Diaminostilbene,  NH2-C0H4-CH:CH-C6H4-NH2,  can  be  ob- 
tained by  treatment  of  p-nitrobenzyl  chloride,  C1H2C 


§  376]  BEN Z I L1C  ACID.  533 

with  alcoholic  potash,  and  subsequent  reduction  of  the  p-dinitro- 
stilbene  thus  formed.  It  is  used  as  a  basis  for  the  preparation  of 
certain  dyes. 

Derivatives  of  dibenzyl  are  got  by  the  condensation  of  benzal- 
dehyde  in  presence  of  potassium  cyanide.  For  example,  benzoin 
is  thus  formed : 

C6H5.C^7°C.C6H5  =  C6H5.CO.CHOH.C6H5. 

Benzoin 

It  has  the  character  of  a  keto-alcohol,  since  it  takes  up  two 
hydrogen  atoms,  with  formation  of  a  dihydric  alcohol,  hydro- 
benzoin,  C6H5.CHOH.CHOH.C6H5.  On  oxidation  it  yields  a 
diketone,  benzil,  C6H5»CO-CO-C6H5.  Benzoin  contains  the  group 
— CHOH-CO — ,  which  is  present  in  the  sugars  (202).  It  also  pos- 
sesses properties  characteristic  of  the  sugars:  thus,  it  reduces  an 
alkaline  copper  solution,  and  yields  an  osazone. 

Benzil  is  a  yellow,  crystalline  substance.  As  a  diketone  it 
unites  with  two  molecules  of  hydroxylamine  to  form  a  dioxime. 

Benzildioxime  exists  in  three  isomeric  forms,  the  number  indi- 
cated by  the  stereoisomerism  of  nitrogen  derivatives  (318): 

CGH5-C C-C0H5    C6H5.C— C-C6H3    C8H5-C C-C6H5 


NOH  NOH     HON  NOH       NOH  HOI 

ampfo'Benzildioxime  anta'Benzildioxime  *\y/tBenzildioxime 

One  of  these  oximes  readily  yields  an  anhydride,  and  is  therefore 
assumed  to  have  the  two  hydroxyl-groups  in  close  proximity,  the 
s?/n-formula.  One  of  the  other  dioximes  is  the  most  stable  of  the 
three  compounds,  and  can  be  obtained  by  various  means.  The 
third  dioxime  can  be  easily  transformed  into  this  stable  modifica- 
tion. It  is  probable  that  the  stable  dioxime  has  the  symmetrical 
or  cm^-formula,  so  that  the  amp/a-formula  must  be  that  of  the 
unstable  modification. 

When  heated  with  alcoholic  potash,  benzil  takes  up  one  mole- 
cule of  water,  undergoing  an  intramolecular  transformation,  with 
production  of  benzilic  acid,  a  reaction  analogous  to  the  formation  of 
pinacolin  from  pinacone  (150)  : 

C6H5.CO.CO.C6H5+H20  =  C6Hs>C<COOH- 

Benailic  acid 


CONDENSED  BENZENE-NUCLEI. 

377.  Condensed-ring  compounds  contain  two  or  more  closed 
chains,  with  C-atoms  common  to  both.  Such  compounds  are  pres- 
ent in  the  higher-boiling  fractions  of  coal-tar  (286).  Next  to  the 
phenols,  naphthalene  is  the  principal  constituent  of  the  second 
fraction,  carbolic  oil,  and  of  the  third  fraction,  creosote-oil.  The 
anthracene-oil  contains  anthracene  and  phenanthrene,  and  other 
hydrocarbons.  These  three  compounds  and  some  of  their  deriva- 
tives will  be  described. 

I.     NAPHTHALENE,  CjoHg. 

Naphthalene  is  present  in  considerable  proportion  in  coal- 
tar,  from  which  it  is  readily  obtained  pure.  On  cooling,  the  crudo 
crystals  of  naphthalene  precipitate  from  the  fraction  distilling 
between  170°  and  230°.  The  liquid  impurities  are  pressed  out,  and 
are  further  eliminated  by  conversion  into  non-volatile  sulphonic 
acids  on  warming  the  crude  product  with  small  quantities  of  con- 
centrated sulphuric  acid,  and  distilling  with  steam  or  subliming. 
The  process  yields  pure  naphthalene. 

Naphthalene  crystallizes  in  shining  plates,  melting  at  80°,  and 
boiling  at  218°.  It  is  insoluble- in  water,  but  readily  soluble  in  hot 
alcohol  and  ether:  it  dissolves  to  a  very  small  extent  in  cold  alcohol. 
It  has  a  characteristic  odour,  and  is  very  volatile.  It  is  always 
present  in  coal-gas,  the  illuminating  power  of  which  is  to  a  large 
extent  due  to  its  presence.  It  is  extensively  employed  in  the 
manufacture  of  dyes. 

The  formation  of  naphthalene  on  passing  the  vapours  of  many 
compounds  through  a  red-hot  tube,  a  process  somewhat  similar  to 
that  which  takes  place  in  the  retorts  of  the  gas-works  (286),  ex- 
plains its  occurrence  in  coal-tar. 

534 


377]  ;  NAPHTHALENE.  535 

.  The  constitution  of  naphthalene  is  proved  in  355  to  be 

H     H 

YYY. 

H\/\/H 

H     H 

This  view  is  confirmed  by  two  syntheses. 

1.  o-Xylylene  bromide  is  converted  by  treatment  with  tetraethyl 
disodioethanetetracarboxylate  into  tetraethyl  hydronaphthalenetetra- 
carboxylate: 

/CH2Br    NaC(COOC2H5)2  /CH2— C(COOC2H5)2 

C0H4(  +       |  ->C6H4( 

\CH,Br    NaC(COOC2H5)2  XCH2— C(COOC2H5)2 

o-Xyiylene  bromide 

On  saponification,  this  compound  loses  two  molecules  of  carbon 
dioxide,  forming  hydronaphthalenedicarboxylic  acid: 

/CH2— CH-COOH 
C6H  /  | 

XCH2— CH-COOH 

The  silver  salt  of  this  acid  readily  gives  up  two  molecules  of  carbon 
dioxide  and  two  atoms  of  hydrogen,  yielding  naphthalene. 

2.  On  heating,  phenylvinylacetic  acid  is  converted  into  a-naph~ 
thol,  a  hydroxy-derivative  of  naphthalene : 

H     CH 

H/\/\CH 


-H20     = 
H\/H    ,CH2 

H  OC/  OH 

HO 

Phenylvinylacetic  acid  a-Naphthol 

Naphthalene  behaves  in  all  respects  as  an  aromatic  hydrocarbon. 
With  nitric  acid  it  yields  a  nitro-derivative;  with  sulphuric  acid  a 
sulphonic  acid:  its  hydro xyl-derivatives  have  the  phenolic  charac- 
ter: the  amino-compounds  undergo  the  diazo-reaction:  etc. 

For  naphthalene,  as  for  benzene  (283)1  no  formula  indicating  its 
internal  structure  and  satisfactorily  accounting  for  its  properties  has 
been  proposed. 


536 


ORGANIC  CHEMISTRY. 


[§  378 


Formula  I.  (Fig.  80)  is  analogous  to  the  centric  formula  for  ben- 
zene: it  is  difficult  to  represent  its  configuration  in  space. 


i. 
FIG.  80. 

FIG.  80. — CENTRIC  NAPHTHALENE-FORMULA. 
FIG.  81. — THIELE'S  NAPHTHALENE-FORMULA. 
FIG.  82. — SIMPLE  NAPHTHALENE-FORMULA. 

THIELE  has  suggested  formula  II.  (Fig.  81),  with  inactive  double 
linkings  (283),  and  of  those  put  forward  it  seems  to  give  the  best 
expression  to  the  properties  of  naphthalene.  The  question  of  what 
formula  most  accurately  represents  the  internal  structure  of  the 
naphthalene  molecule  is,  however,  of  no  practical  importance,  for, 
the  simple  scheme  III.  (Fig.  82),  which  leaves  the  problem  unsolved 
fully  accounts  for  the  isomerism  of  the  derivatives  of  naphthalene. 

As  with  benzene,  partial  hydrogenation  of  naphthalene  changes 
its  characteristic  aromatic  character;  for  naphthalene  dihydride, 
CioHjo,  adds  bromine  as  readily  as  compounds  with  double 
linkings. 

378.  Naphthalene  yields  a  much  greater  number  of  substitu- 
tion-products than  benzene,  the  number  obtained  corresponding 
with  those  theoretically  possible  for  a  compound  with  the  for- 
mula in  377.  This  fact  supports  the  constitution  indicated. 

A  compound  of  the  formula 


H 


must  yield  two  isomeric  monosubstitution-products.  Substitution 
can  take  place  at  a  carbon  atom  directly  linked  to  one  of  the  two 
C-atoms  common  to  both  rings  (1,  4,  5,  or  8),  or  at  one  of  the  others 
(2,  3,  6,  or  7),  which  are  also  similar  to  one  another.  Two  series 
of  monosubstitution-products  are  in  fact  known:  those  in  which 


§378]  NAPHTHALENE.  537 

the  hydrogen  at  1,4,  5,  or  8  has  been  replaced  are  called  a-deriva- 
tives;  when  hydrogen  is  substituted  at  2,  3,  6,  or  7,  the  products 
are  termed  /3-derivatives. 

A  great  number  of  disubstitution-products  is  possible:  for  two 
similar  substituents  it  is  10,  and  for  two  dissimilar  substituents  14. 
Many  of  them  have  been  obtained.  The  ten  isomerides  are  denoted 
by  the  numbers 

1:2,  1:3,  1:4,  1:5,  1:6,  1:7,  1:8,  2:3,  2:6,  2:7. 

In  any  other  arrangement  the  grouping  is  identical  with  one  of 
these:  thus,  2:5=1:6,  and  3:6  =  2:7,  etc.  For  three  similar  sub- 
stituents the  number  of  possible  isomerides  is  much  greater,  and 
still  greater  for  three  dissimilar  ones.  The  disubstitution-products 
with  the  substituents  in  the  same  ring  are  called  ortho,  meta,  and 
para.  When  they  are  in  different  rings,  the  compounds  are  usually 
distinguished  by  numbers,  or  sometimes  by  letters:  thus,  a  com- 
pound 4 : 5  is  also  denoted  by  aaf,  and  one  3 : 6  by  /?/?'.  The  positions 
1:8  and  4:5  are  also  called  the  pen-positions :  in  certain  respects 
they  resemble  the  or^o-positions.  For  example,  peri-naphthalenedi- 
carboxylic  acid, 

OOH 

OOH' 


resembles  o-phthalic  acid  in  its  ability  to  form  an  anhydride. 

On  account  of  the  great  number  of  isomerides,  the  orienta- 
tion of  naphthalene  derivatives  is  sometimes  difficult,  and  the 
positions  occupied  by  the  substituents  in  many  compounds  are  still 
uncertain.  The  same  method  of  orientation  is  employed  as  for  the 
benzene  derivatives,  the  conversion  of  compounds  with  side-chains 
in  unknown  positions  into  others  with  substituents  in  positions 
that  have  been  determined. 

Oxidation  is  another  important  aid  in  their  orientation,  and  is 
employed  to  determine  whether  the  substituents  are  attached  to 
the  same  ring,  or  to  different  rings,  as  well  as  their  position  relative 
to  one  another.  Thus,  suppose  the  position  of  the  nitro-groups 
in  a  dinitronaphthalene  has  to  be  determined.  If  it  yields  phthalic 


538  ORGANIC  CHEMISTRY,  [§379 

acid  on  oxidation,  the  two  nitro-groups  must  be  in  union  with  the 
same  ring,  that  one  which  has  been  removed  by  oxidation.  If  a 
dinitrophthalic  acid  is  formed,  this  also  proves  that  the  two  nitro- 
groups  are  linked  to  the  same  ring,  and  the  orientation  of  these 
groups  in  this  acid  should  indicate  their  relative  position  in  the 
naphthalene  derivative.  Lastly,  if  oxidation  yields  a  mononitro- 
phthalic  acid,  one  nitro-group  is  attached  to  each  ring,  and  orienta- 
tion of  the  mononitrophthalic  acid  obtained  will  determine  the 
position  of  one  of  the  nitro-groups. 


Substitution-products. 

379.  The  homologues  of  naphthalene  —  methyl-derivatives, 
ethyl-derivatives,  etc. — are  unimportant.  They  can  be  prepared 
by  FITTIG'S  method,  or  that  of  FRIEDEL  and  CRAFTS  (287,  1  and  2). 

a-Methylnaphthalene  is  a  liquid,  and  boils  at  240°-242° :  /?-methyl- 
naphthalene  is  a  solid,  and  melts  at  32°.  Both  are  present  in  coal- 
tar.  On  oxidation,  they  yield  a-naphthoic  acid  and  (3-naphthoic  acid 
respectively,  which  resemble  benzoic  acid  in  their  properties.  They 
are  converted  into  naphthalene  by  distillation  with  lime. 

a-Chlvronaphthalene  and  a-bromonaphthalene  are  respectively 
formed  by  the  action  of  chlorine  and  bromine  upon  boiling  naph- 
thalene. Although  their  halogen  atom  is  not  so  firmly  linked  as 
that  in  monochlorobenzene  or  monobromobenzene  (289),  they  are 
not  decomposed  by  boiling  with  alkalis.  A  similar  stability  charac- 
terizes the  corresponding  /^-compounds,  which  are  not  obtained  by 
the  direct  action  of  halogens  upon  naphthalene,  but  can  be  pre-, 
pared  from  others-compounds,  such  as  amino-derivatives,  sulpho- 
derivatives,  etc.,  by  the  methods  described  under  benzene  (292, 
293,  and  307,  4). 

The  product  obtained  by  the  action  of  concentrated  nitric 
acid  upon  naphthalene  is  very  important  for  the  orientation  of 
the  naphthalene  derivatives.  It  is  a-nitronaphthalene,  M.P.  61°, 
which  is  proved  to  belong  to  the  a -series  by  its  conversion  into 
the  same  naphthol  as  is  obtained  from  phenylvinylacetic  acid  (377) . 

The  position  of  the  substituents  in  a  great  number  of  mono- 
substitution-products  can  be  determined  from  a  knowledge  of  that 
of  the  nitro-group  in  this  nitronaphthalene,  for  the  nitro-group 


§  379]         NAPHTHALENE  SUBSTITUTION-PRODUCTS.  539 

can  be  reduced  to  an  amino-group,  which  is  replaceable  by  numer- 
ous atoms  or  groups  by  means  of  the  diazo-reaction.  If  a  mono- 
substituted  naphthalene  is  known  to  be  an  a -compound,  its  iso- 
meride  must  belong  to  the  /2-series. 

a-Nitronaphthalene  is  a  yellow,  crystalline  compound,  and 
melts  at  61°.  The  corresponding  /^-compound  is  similar,  and 
melts  at  79°.  It  is  obtained  by  diazotizing  2-nitro-a-naphthyl- 
amine. 

On  heating  naphthalene  with  concentrated  sulphuric  acid 
at  a  temperature  not  exceeding  80°,  a-naphthalenemonosulphonic 
acid  is  chiefly  formed :  at  160°  the  /2-acid  is  the  principal  product, 
owing  to  the  conversion  of  the  a-compound  into  its  #-isomeride. 
Both  are  crystalline  and  very  hygroscopic. 

On  fusion  with  caustic  potash,  the  naphthalenesulphonic  acids 
are  converted  into  naphthols,  CioH7-OH,  with  properties  very  simi- 
lar to  those  of  phenol.  They  are  present  in  coal-tar.  a-Naphthol 
melts  at  95°,  and  boils  at  282°:  j^-naphthol  melts  at  122°,  and  boils 
at  288°.  The  hydroxyl-group  in  these  compounds  can  be  replaced 
much  more  readily  than  that  in  phenol.  They  dissolve  in  alkalis. 
With  ferric  chloride  a-naphthol  yields  a  flocculent,  violet  precipi- 
tate: /?-naphthol  gives  a  green  coloration,  and  a  precipitate  of 
f)-dinaphthol,  •  HO.CioH6.C10H6-OH.  The  violet  precipitate 
obtained  with  a-naphthol  is  possibly  an  iron  derivative  of 
«-dinaphthol. 

a-Naphthylamine  and  /3-naphthylfimine,  CioH7*N"H2,  can  be 
obtained  by  the  reduction  of  the  corresponding  nitro-derivatives, 
but  are  usually  prepared  by  heating  a-naphthol  and  /?-naphthoI 
respectively  with  the  ammonia  compound  of  zinc  chloride  or  of 
calcium  chloride.  a-Naphthylamine  is  a  solid  and  is  also 
formed  by  heating  naphthalene  with  sodamide,  NH2Na, 
above  200°,  hydrogen  being  evolved.  It  melts  at  50°,  and 
has  a  fsecal-like  odour:  /?-naphthylamine  melts  at  112°,  and  is 
nearly  odourless.  A  mode  of  distinguishing  between  the  isomerides 
is  afforded  by  the  fact  that  the  salts  of  the  a-compound,  but  not 
the  ^-compound,  give  a  blue  precipitate  with  ferric  chloride  and 
other  oxidizing  agents. 

These  bases  are  of  technical  importance,  since  the  dyes  of  the 
congo-group  and  the  benzopurpurins  are  derived  from  them,  and  pos- 
sess the  important  property  of  dyeing  unmordanted  cotton. 

Congo-red  is  formed  by  diazotizing  benzidine,  and  treating  the 


540  ORGANIC    CHEMISTRY.  [§  38o 

product  with  a  sulphonic   acid   of   naphthylamine.     The  dye  is  the 
sodium  salt  of  the  acid  thus  formed : 


Benzidine  Benzidinediazonium  chloride       Naphthylaminesul- 

phonic  acid 


Congo-red 

The  acid  itself  is  blue. 

The  benzopurpurins  differ  from  congo-red  only  in  having  a 
methyl-group  attached  to  each  benzene-nucleus  of  the  benzidine- 
group. 

380.  Among  the  polysubstituted  naphthalene  derivatives  is 
2*4:-dinitro-a-naphthol,  obtained  by  the  action  of  nitric  acid  upon 
the  monosulphonic  or  disulphonic  acid  of  a-naphthol.  Its  sodium 
salt  is  Marlins's  yellow:  »it  dyes  wool  and  silk  directly  a  golden- 
yellow.  Nitration  of  a-naphtholtrisulphonic  acid  yields  dinitro- 
naphtholsulphonic  acid,  the  potassium  salt  of  which  is  naphthol- 
yellow:  it  resists  the  action  of  light  better  than  Martius's  yellow. 

Naphthionic  acid  is  one  of  the  longest-known  naphthalene 
derivatives.  It  is  1 : 4-naphlhylaminesulphonic  acid, 


SO,H 


NH2 

and  results  from  the  interaction  of  a-naphthylamine  and  sulphuric 
acid.     It  is  crystalline,  and  only  slightly  soluble  in  water.     It  is 
manufactured   for  the  preparation  of  congo-red  and  other  dyes. 
Solutions  of  its  salts  display  an  intense  reddish-blue  fluorescence. 
Three  quinones  of  naphthalene  are  known : 

O  0 

/V\.       |/V%0  /V>° 

\AX    °\AA 

6  6 

/J  amphi  Benzoquinone 


§381]  NAPHTHAQUINONES.  541 

a-N  aphthaquinone ,  CioHeC^,  is  formed  by  the  oxidation  of 
many  a -derivatives,  and  of  some  di-derivatives,  of  naphthalene. 
It  is  usually  prepared  from  naphthalene  itself  by  oxidation  with 
a  boiling  solution  of  chromic  acid  in  glacial  acetic  acid,  a  method 
of  formation  which  has  no  parallel  among  those  for  the  prepara- 
tion of  the  corresponding  benzene  derivatives.  It  crystallizes 
from  alcohol  in  deep-yellow  needles,  melting  at  125°.  On  oxi- 
dation, it  yields  phthalic  acid,  proving  both  oxygen  atoms 
to  be  attached  to  the  same  ring.  With  hydroxylamine  it  yields 
an  oxime.  Knowing  the  structure  of  a-naphthaquinone,  it  is 
possible  to  determine  that  of  other  di-derivatives.  "If,  on  oxida- 
tion, they  yield  this  quinone  by  elimination  of  the  substituents, 
they  must  be  l:4-derivatives. 

ft-Naphthaquinone,  CioHeC^,  is  formed  by  oxidation  of  1:2- 
aminonaphthol. 

amphi-Naphthaquinone,  or  2 : 6-naphthaquinone,  is  obtained  by 
oxidation  of  a  benzene-solution  of  the  corresponding  dihydroxy- 
naphthalene  with  lead  peroxide. 

The  structural  formula  indicate  that  only  in  the  amphi- 
isomeride  is  the  arrangement'  of  the  CO-groups  relative  to  the 
double  bonds  similar  to  that  in  benzoquinone ;  and  these  two 
quinones  are  very  similar  in  chemical  character.  Both  oxidize 
at  once  a  cold,  dilute  solution  of  hydriodic  acid,  turn  ferrous 
ferrocyanide  blue,  and  oxidize  sulphurous  acid.  a-Naphtha- 
quinone  exhibits  none  of  these  characteristics,  but  resembles 
benzoquinone  in  odour  and  volatility.  /?-Naphthaquinone  does 
not  oxidize  dilute  hydriodic  acid,  but  turns  ferrous  ferrocyanide 
blue,  and  oxidizes  sulphurous  acid.  Like  the  amp/M-derivative 
it  is  non-volatile,  and  therefore  odourless.  Each  of  the  naphtha- 
quinones  has  a  red  colour. 

Addition-products. 

381.  Naphthalene  and  its  derivatives  yield  addition-products 
somewhat  more  readily  than  the  benzene  derivatives. 

All  the  intermediate  hydrogenation-products  of  naphthalene  from 
dihydronaphthalene,  C10H10,  to  dodecahydronaphthalene,  C10H2(b  are 
known,  each  member  having  two  hydrogen  atoms  more  than  its 
immediate  predecessor.  The  first-named  is  obtained  by  the  action  of 


542 


ORGANIC   CHEMISTRY. 


[§381 


sodium  and  alcohol  upon  naphthalene.     Oxidation  converts  it  into 
o-phenylenediacetic  acid: 


H     H 


H      H2 


H 


'H 


H 

Naphthalene 


H     H2 

Dihydnde 


CH2.COOH 
CH2'COOH* 

o-Phenylenediacetic  acid 


Assuming  that  the  formula  given  represents  naphthalene,  the  hydro- 
gen is  added  to  the  conjugated  double  linking  at  the  positions  1 :4. 

When  reduced  with  sodium  and  boiling  amyl  alcohol,  /?-naph- 
thylamine  yields  a  tetrahydride,  CioHnNH2,  a  compound  with 
most  of  the  properties  characteristic  of  the  aliphatic  amines:  it  is 
strongly  alkaline,  absorbs  carbon  dioxide  from  the  air,  has  an 
ammoniacal  odour,  and  cannot  be  diazotized.  All  four  hydrogen 
atoms  are  in  union  with  the  same  ring  as  the  amino-group, 


HNH2 


H     H2 


since,  on  oxidation  with  potassum  permanganate,  the  compound 
converted  into  the  o-carboxylic  acid  of  dihydrocinnamic  acid, 


COOH 


which  must  evidently  result  from  a  tetrahydride  with  the  above 
structure  if  the  oxidation  takes  place  at  the  C-atom  linked  to  the 
NH2~group.  Moreover,  the  hydrogen  addition-product  does  not 
take  up  bromine,  another  proof  that  the  four  H-atoms  are  attached 
to  the  same  benzene-nucleus.  The  entrance  of  two  hydrogen  atoms 
into  each  ring  would  produce  a  compound  with  double  bonds, 
capable  of  yielding  an  addition-product  with  bromine. 

The  reduction-product  may,  therefore,  be  regarded  as  benzene 


§381]  NAPHTHYLAMINES.  543 

with  a  saturated  side-chain,  —  CH2.CH2-CH(NH2)-CH2— ,  linked 
to  two  or^o-C-atoms. 

a-Naphthylamine  can  also  be  reduced  by  amyl  alcohol  and 
sodium,  but  the  tetrahydride  formed  is  different  in  character  from 
that  obtained  from  /?-naphthylamine,  for  it  possesses  all  the  proper- 
ties characteristic  of  the  aromatic  amines:  it  can  be  diazotized, 
and  has  no  arnmoniacal  odour.  Since,  like  ^-naphthylamine,  it 
forms  no  addition-product  with  bromine,  its  constitution  is 


which  proves  that  the  four  hydrogen  atoms  in  it  likewise  are  in 
union  with  the  same  nucleus,  but  not  the  one  linked  to  the  amino- 
group.  In  support  of  this  view  are  its  completely  aromatic 
character,  and  the  fact  that,  on  oxidation  with  potassium  per- 
manganate, the  ring  containing  the  amino-group  is  removed,  with 
formation  of  adipic  acid  (161), 

CH2 

/\ 
CH2  COOH 


2  COOH 

\/ 
CH2 

a-Naphthylamine  tetrahydride  must,  therefore,  be  looked  upon  as 
aniline  containing  a  saturated  side-chain,  — CH2.CH2-CH2-CH3 — , 
linked  to  two  or^o-C-atoms. 


The  molecular  refraction  of  benzylamine  is  34*12,  the  calculated 
being  34-30;  the  corresponding  values  for  aniline  are  30-27 
and  29-72.  These  facts  prove  the  refraction  of  benzylamine  to  be 
normal;  but  that  of  aniline  to  be  abnormal,  with  an  exaltation  of 
0-55.  A  similar  discrepancy  characterizes  the  reduction-products  of 
a-naphthylamine  and  /3-naphthylamine.  The  molecular  refraction 


544 


ORGANIC  CHEMISTRY. 


382 


calculated  for  both  is  45  •  80 :  the  experimental  value  for  the  a-com- 
pound  containing  an  aromatic  ammo-group,  is  46*66;  and  that  for 
the  j3-compound,  with  an  aliphatic  amino-group,  is  45-88.  Only  the 
amine  of  aromatic  character  exhibits  an  exalted  molecular  refrac- 
tion. This  example  furnishes  further  evidence  of  the  value  of 
molecular  refraction  in  deciding  questions  of  structure. 


II.   ANTHRACENE,  Ci4Hi0. 

382.  Anthracene  is  present  only  in  small  proportions  in  coal- 
tar,  varying  between  0-25  andO«45  per  cent.;  nevertheless,  it  is 
the  basis  of  the  manufacture  of  the  important  dyestuff,  alizarin 

(385)- 

The  so-called  "  50  per  cent,  anthracene,"  obtained  by  distilling 
anthracene-oil  (286),  is  distilled  with  one-third  of  its  weight  of 
potassium  carbonate  from  an  iron  retort.  Certain  impurities  are 

0*  TT 

thereby   removed,   among   them   carbazole,    -6    4>NH,   which   is 

C6H4 

present  in  considerable  proportion  in  the  crude  anthracene,  and 
is  thus  converted  into  a  non-volatile  potassium  derivative, 
(C6H4)2N-K.  The  distillate  consists  almost  entirely  of  anthracene 
and  phenanthrene:  it  is  treated  with  carbon  disulphide,  which 
dissolves  out  the  phenanthrene.  By  crystallization  from  benzene, 
the  anthracene  is  obtained  pure. 

It  crystallizes  in  colourless,  glistening  leaflets,  with  a  fine  blue 
fluorescence.  It  melts  at  213°,  and  boils  at  351°.  It  dissolves 
readily  in  boiling  benzene,  but  with  difficulty  in  alcohol  and  ether. 
With  picric  acid  it  yields  a  compound  C^H^o'CeH^NC^XsOH, 
melting  at  138°. 

On  exposure  to  light,  anthracene  is  transformed  into  dianthracene, 
which  in  the  dark  becomes  depolymerized  to  anthracene,  one  of  the 
rare  instances  of  a  reversible  photochemical  reaction: 


Light 


2C14H10 

Dark 

Several  modes  of  preparing  anthracene  are  known  which  give 
an  insight  into  its  constitution.     One  of  these  is  its  synthesis  by 


§  383]  ANTHRACENE.  545 

ANSCHUTZ'S  method  from  benzene,  aluminium  chloride,  and  tetra- 
bromoethane : 

BrCHBr  CHV 

C6H6+      |          +  C6H6   =  =  C6H4<  |      >C6H4  +  4HBr. 
BrCHBr  XCH/ 

This  synthesis  proves  that  anthracene  contains  two  benzene- 
nuclei  united  by  the  group  C2H2,  linked  to  two  or//&0-C-atoms  of 
each,  as  proved  for  anthraquinone  in  383.  Its  constitutional 
formula  is 


Anthracene 

It  follows  that  it  must  yield  a  very  large  number  of  isomeric 
substitution-products.  Three  monosubstitution-products  are 
possible.  Numbering  the  carbon  atoms  as  in  the  formula, 
then  1  =  4  =  5  =  8,  2  =  3  =  6  =  7,  and  9=10.  Fifteen  disubstitution- 
products  with  similar  groups  are  possible.  A  very  considerable 
number  of  anthracene  derivatives  is  known,  although  it  is  small 
in  comparison  with  the  enormous  number  theoretically  possible. 

The  orientation  of  the  anthracene  derivatives  is  effected  simi- 
larly to  those  of  naphthalene  (377),  oxidation  and  a  study  of  the 
resulting  products  being  an  important  aid. 

Substitution-products. 

383.  Anthraquinone,  C^HgC^,  is  one  of  the  most  important 
derivatives  of  anthracene,  from  which  it  is  obtained  by  oxidation 
with  such  agents  as  nitric  acid  and  chromic  acid.  Anthracene  is  so 
readily  converted  into  anthraquinone  by  nitric  acid  that  it  is  not 
possible  to  nitrate  it. 

Anthraquinone  is  proved  to  have  the  structure 

CO 

\ 
CO 


546  ORGANIC  CHEMISTRY.  [§  383 

since  it  is  formed  by  the  interaction  of  phthalic  anhydride  and 
benzene  in  presence  of  a  dehydrating  agent  such  as  aluminium 
chloride : 

C6H4  <  co  >  |Q  +  H2|C6H4  =  C6H4  <  £Q  >C6H4  +H2O. 

Phthalic  anhydride 

The  reaction  takes  place  in  two  stages:    o-benzoylbenzoi'c  acid, 

'•P  IT 

^VT   5,  is  first  formed,  and  then  loses  one  molecule  of 

water,  forming  anthraquinone*. 

CO 

C6H4/\C6H5  -  H20  -  C6H4<£°>C6H4. 
\COOH 

The  constitutional  formula  of  anthraquinone  indicates  that  only 
two  isomeric  monosubstitution-products  are  possible.  This  has 
been  verified  by  experiment — a  further  proof  that  the  formula  is 
correct. 

The  central  groups  in  anthraquinone,  and  hence  those  in  anthra- 
cene, can  be  proved  to  be  in  union  with  two  o-C-atoms  in  each 
benzene-nucleus.  The  method  is  similar  to  that  employed  in  prov- 
ing the  constitution  of  naphthalene  (355),  the  marking  of  one  of  the 
nuclei  by  the  introduction  of  a  substituent  affording  a  means  of 
identifying  the  nucleus  eliminated  by  oxidation. 

On  treatment  with  benzene  and  aluminium  chloride,  bromo- 
phthalic  anhydride  reacts  analogously  to  phthalic  anhydride,  yield- 
ing bromoanthraquinone  by  elimination  of  water  from  the  bromo- 
benzoylbenzoic  acid  first  formed: 


/C0\  i.    /C0\    ii. 

O  -»  Br-C6H3<  NC6H6 


3 
\COOH 

Bromophthalic  anhydride         Bromobenzoylbenzoic  j          >CO\       II 


Br.C6H3 


\ 

C6H4. 


Bromoanthraquinone 

Since  bromoanthraquinone  is  a  derivative  of  phthalic  acid,  its  two 
carbonyl-groups  must  be  united  to  two  o-C-atoms  of  nucleus  I. 


384]  ANTHRAQUINONE.  .347 

Its  Br-atom  can  be  replaced  by  a  hydroxyl-group  by  heating  with 
potassium  carbonate  at  160°,  and  the  hydroxyanthraquinone  thus 
formed  can  be  oxidized  to  phthalic  acid  by  the  action  of  nitric  acid. 
These  transformations  prove  nucleus  II.  to  be  unattacked,  and  to 
have  the  two  carbonyl-groups  attached  to  o-C-atoms: 


HO-CHS 


/ 


ii.  HOCCK 

/CeH4      —>  / 


/CeH4 

/ 


HO  -CO 

Hydroxyanthraquinone  Phthalic  acid 

384.  Anthraquinone  crystallizes  from  glacial  acetic  acid  in 
light-yellow  needles,  melting  at  277°.  At  higher  temperatures  it 
sublimes  very  readily,  forming  long,  sulphur-yellow  prisms.  It  is 
very  stable,  and  is  not  easily  attacked  by  oxidizing  agents,  or  by 
concentrated  nitric  acid  or  sulphuric  acid. 

The  name  anthragwmone  is  in  soms  measure  incorrect,  for  this 
substance  lacks  some  of  the  properties  characteristic  of  quinones, 
such  as  being  easily  reduced,  great  volatility,  pungent  odour,  etc., 
and  has  much  more  the  character  of  a  diketone.  With  fused 
potassium  hydroxide  it  yields  benzole  acid,  and  with  hydroxyl- 
amine  an  oximc.  On  warming  with  zinc-dust  and  sodium- 
hydroxide  solution,  it  forms  the  disodium-derivative  of  anthra- 
quinol, 

COH 


COH 

Anthraquinol  forms  brown  crystals  melting  at  180°,  its  solutions 
exhibiting  an  intense  green  fluorescence.  Its  alkaline  solution 
has  a  deep  blood-red  colour,  and  in  this  condition  it  is  converted 
into  anthraquinone  by  atmospheric  oxidation. 

This  property  of  anthraquinol  makes  its  formation  a  delicate  test 
for  anthraquinone.  It  is  effected  by  warming  the  substance  to  be 
tested  with  zinc-dust  and  sodium-hydroxide  solution:  if  anthra- 
quinone is  present,  a  blood-red  coloration  is  developed,  and  is 
destroyed  by  agitating  the  mixture  with  air. 

Isomeric  with  anthraquinol  is  a  ketonic  compound,  oxanthrone, 

CO 


/c\ 

H        OH 


548  ORGANIC  CHEMISTRY.  [§  385 

It  is  converted  by  a  cold  alcoholic  solution  of  hydrogen  chloride 
into  anthraquinol  to  the  extent  of  97  per  cent.,  the  same  reagent 
effecting  the  inverse  transformation  of  anthraquinol  into  oxanthrone 
to  the  extent  of  3  per  cent.  Oxanthrone  melts  at  167°,  is  colour- 
less, and  does  not  exhibit  fluorescence  in  solution.  Anthraquinol 
and  oxanthrone  exemplify  a  type  of  desmotropy  characterized  by 
the  great  stability  of  both  forms. 

On  reduction  with  tin  and  hydrochloric  acid,  anthraquinone  is 
converted  into  anthrone, 

CO 


CH2 

a  substance  converted  by  boiling  with  alkalis  into  the  tautomeric 
anthranol, 

C-OH 

C6H4</[>C6H4. 
CH 


In  solution,  anthranol  exhibits  a  bright-blue  fluorescence.  It  is 
readily  reconverted  into  anthrone,  and  anthranol  is  also  produced 
to  some  extent  by  boiling  anthrone  with  dilute  acetic  acid. 
Anthrone  is  to  be  regarded  as  a  pseudo-acid,  anthranol  being  its 
aci-form. 

When  anthraquinone  is  more  strongly  reduced,  by  heating 
with  zinc-dust,  it  yields  anthracene. 

385.  Alizarin,  or  dihydroxyanthraquinone,  Ci4H602(OH)2,  is 
the  most  important  derivative  of  anthraquinone,  and  is  a  dye  of 
a  splendid  red  colour.  It  was  formerly  manufactured  from  mad- 
der-root, which  contains  a  glucoside,  ruberythric  acid,  C26H28O14. 
When  boiled  with  dilute  sulphuric  acid  or  hydrochloric  acid,  this 
glucoside  yields  dextrose  and  alizarin: 


2H20  =  2C6H1206  +  C14H602  (OH)  2. 

Ruberythric  acid  Dextrose  Alizarin 

The  dye  is  now  prepared  almost  wholly  by  a  synthetical  method 
It  is  one  of  the  organic  dyestuffs  known  in  antiquity. 


§  385]  ALIZARIN.  549 

In  preparing  alizarin,  the  anthracene  is  first  oxidized  to  anthra- 
quinone  with  sodium  dichromate  and  sulphuric  acid.  Heating 
with  concentrated  sulphuric  acid  at  100°  converts  various  impur- 
ities into  sulphonic  acids,  the  anthraquinone  remaining  unchanged : 
on  dilution,  these  sulphonic  acids  dissolve,  so  that  pure  anthra- 
quinone is  left  after  filtering.  This  is  then  heated  to  160°  with 
fuming  sulphuric  acid  containing  50  per  cent,  of  sulphur  trioxide, 
the  main  product  being  the  monosulphonic  acid. 

It  is  remarkable  that  the  a-sulphonic  acid  is  formed  in  presence 
of  a  mercury  salt,  but  that  otherwise  the  /3-sulphonic  acid  is  the 
product.  Catalysts  very  rarely  exert  an  influence  of  this  type. 

The  sodium  salt  of  the  sulphonic  acid  is  only  slightly  soluble 
in  water,  and  separates  out  when  the  acid  is  neutralized  with 
sodium  carbonate.  On  fusing  with  sodium  hydroxide,  the  sulpho- 
group  is  replaced  by  hydroxyl.  A  second  hydroxyl-group  is 
simultaneously  formed,  its  production  being  considerably  facil- 
itated by  the  addition  to  the  reaction-mixture  of  potassium 
chlorate  as  an  oxidizing  agent: 


C6H4<£°>C6H3.S03Na+3NaOH+0  = 

Sodium  anthraquinone- 
monosulphonate 

=  C6H4<">C6H2(ONa)2+2H20+Na2S03. 


The  dye  is  liberated  from  the  sodium  salt  by  addition  of  an  acid. 

Anthraquinone  can  be  directly  oxidized  to  alizarin  by  heating 
it  with  very  concentrated  aqueous  alkali  in  presence  of  certain 
oxidizers,  such  as  mercuric  oxide,  potassium  chlorate,  and  so  on. 

Alizarin  crystallizes  in  red  prisms,  and  sublimes  in  orange 
needles,  melting  at  289°-290°.  It  is  almost  insoluble  in  water,  and 
slightly  soluble  in  alcohol.  On  account  of  its  phenolic  character, 
it  dissolves  in  alkalis.  It  yields  a  diacetate.  On  distillation  with 
zinc-dust,  it  is  converted  into  anthracene,  a  reaction  which  gave 
the  first  insight  into  the  constitution  of  alizarin. 

The  value  of  alizarin  as  a  dye  depends  upon  its  power  of  forming 
with  metallic  oxides  fine-coloured,  insoluble  compounds,  called 


550  ORGANIC  CHEMISTRY.  [§  385 

lakes.  When  a  fabric  is  mordanted  with  one  of  these  oxides,  it 
can  be  dyed  with  alizarin,  the  colour  depending  on  the  oxide  used. 
The  ferric-oxide  compound  of  alizarin  is  violet-black,  the  chromium- 
oxide  compound  claret-colour,  the  calcium-oxide  compound  blue, 
the  aluminium-oxide  and  tin-oxide  compounds  various  shades  of 
red  (Turkey-red),  and  so  on. 

The  method  by  which  alizarin  is  prepared  proves  it  to  be  a 
derivative  of  anthraquinone,  but  the  positions  of  the  hydroxyl- 
groups  have  still  to  be  determined.  The  formation  of  alizarin  when 
phthalic  anhydride  is  heated  at  150°  with  catechol  and  sulphuric 
acid  proves  that  both  are  in  the  same  benzene-nucleus;  and,  since 
the  hydroxyl-groups  in  catechol  occupy  the  o-position,  the  same 
must  be  true  of  alizarin: 

CO>O+C  H4<OH  1  =  c  H4<CO>C  H  <OH  1 

Phthalic  anhydride  Catechol  Alizarin 

It  follows  that  the  choice  lies  between  the  two  structural  formulae 

O      OH  0 

OH  /\/\/\OH 

I.  and  II. 


The  result  of  nitration  proves  that  formula  I.  is  correct.  Two 
isomeric  mononitro-derivatives  are  obtained,  each  with  the  nitro- 
group  in  the  same  nucleus  as  the»hydroxyl-groups,  since  both  can 
be  oxidized  to  phthalic  acid.  Formula  I.  alone  admits  of  the  for- 
mation of  two  such  mononitro-derivatives,  and  must  therefore  be 
correct. 

Other  hydroxy-derivatives  of  anthraquinone  are  also  dyes,  aa 
example  being  purpurin  or  5:6:8-trihydroxyanthraquinone, 

C6H4<(CO)2>C6H(OH)3, 

a  constituent  of  madder-root.  The  power  of  the  hydroxyanthraqui- 
nones  to  form  dyes  with  mordants  is  conditioned  by  the  presence 
of  two  hydroxyl-groups  in  the  ortho-position  to  one  another.  Other 


386]  PHENANTHRENE.  551 

anthraquinone  derivatives  with  hydroxyl-groups  and  amino-groups, 
or  with  amino-groups  only,  are  also  valuable  dyes. 

The   very   fast,   brilliant   colours   of   the   indanthren-group   are 
derivatives  of  2-aminoanthraquinone, 


being  obtained  by  its  oxidation.    Indanthren-blue  is   supposed   to 
have  the  structural  formula 


HI.  PHENANTHRENE,  C14H10. 

386.  Phenanthrene  is  isomeric  with  anthracene,  and  is  present 
with  it  in  "  anthracene-oil."  They  are  separated  by  the  method 
already  described  (382).  It  crystallizes  in  colourless,  lustrous 
plates,  which  dissolve  in  alcohol  more  readily  than  anthracene, 
yielding  a  blue  fluorescent  solution.  It  melts  at  96°,  and  boils  at 
340°. 

On  oxidation  with  chromic  acid,  it  yields  first  phenanthra~ 
quinone,  and  then  diphenic  acid  (372), 


OOC 


HOOC          COOH 


This  reaction  proves  that  phenanthrene  possesses  two  benzene- 
nuclei  directly  linked  to  one  another,  and  is  therefore  a  diphenyl- 
derivative,  and  also  a  di-or^o-compound.  Diphenyl  with  two 
hydrogen  atoms  substituted,  —  C6H4.C6H4  —  ,  or  —  Ci2H8—  ,  differs 


552  ORGANIC  CHEMISTRY.  (§386 

from  phenanthrene  by  C2H2.     This  must  link  together  two  o-posi- 
tions,  so  that  phenanthrene  has  the  constitution 


\ 


This  structure  finds  support  in  the  conversion  of  stilbene  into 
phenanthrene,  on  passing  its  vapour  through  a  red-hot  tube,  a 
method  of  formation  analogous  to  that  of  diphenyl  from  benzene 
(371) : 

CH — CgHs  CH — 

II  -H.-II 

— CeHs  CH — 

Stilbene  Phenanthrene 


\~> 

Ji 


In  the  formula  of  phenanthrene  the  group  — CH=CH — 
and  the  four  carbon  atoms  of  diphenyl  yield  a  third  ring  of  six 
carbon  atoms.  This  ring  is  distinguished  from  a  true  benzene- 
ring  by  the  facts  that  the  C2H2-group  readily  takes  up  bromine, 
and  that  on  oxidation  it  behaves  as  an  ordinary  side-chain. 
C6H4— CO 

Phenanthraquinone ,  ,  is  an  orange,  crystalline  sub- 

C6H4— CO 

stance,  melting  at  200°,  and  boiling  without  decomposition  above 
360°.  Its  diketonic  character  follows  from  its  yielding  di-deriva- 
tives  with  sodium  hydrogen  sulphite  and  with  hydroxylamine.  It 
is  odourless,  and  non-volatile  with  steam. 

PSCHORR  has  discovered  an  important  synthesis  of  phenan- 
threne and  its  derivatives,  the  condensation  of  o-nitrobenzalde- 
hyde  with  phenylacetic  acid  by  the  PERKIN  reaction  (328) : 


/N°2 

/  X 

s     =     H20-hC6H<  X 

\CH:C< 
COOH  XX)OH 

o-Nitro-  Phenylacetic  acid  a-Phenyl-o-nitrocinnamic  acid 

benzaldehyde 


§  386]  PHENANTHRENE.  553 

On  diazotization  of  the  corresponding  amino-acid  obtained  by 
reduction,  and  treatment  in  sulphuric-acid  solution  with  copper- 
dust  (307),  nitrogen  and  water  are  eliminated,  and  an  almost 
quantitative  yield  of  [3-phenanthrenecarboxylic  acid  obtained: 


V/1N2 


CH  CH  CH 

/W-COOH 

OCOOH    ->     I     I     1  -» 


Xn.i 


Ofij 


H 


\ 
I 
\/ 

Diazo-derivative  of  a-phenyl-  Phenanthrene-  Phenanthrene 

o-aminocinnamic  acid  carboxylic  acid 


On  distillation,  this  acid  loses  carbon  dioxide,  forming  phenan- 
threne. 

When  the  methyl  ether  of  o-nitrovanillin  is  substituted  for 
o-nitrobenzaldehyde,  there  results  a  dimethoxyphenanthrene, 
dimethylmorphol,  also  formed  by  the  breaking  down  of  morphine 

CH 

/\  /CHO  /X/Vr-rnoTT 

,H2C'COOH 

JWA.  _, 

OCH,f 

\/ 


N02  I  ->  \/\/\ 


Methyl  ether  of 
o-nitrovanillin 


CH3Oi 

OCH3| 

\/ 

Dimethylmorphol 


B.     HETEROCYCLIC    COMPOUNDS. 


NUCLEI    CONTAINING   NITROGEN,  OXYGEN,  AND 
SULPHUR. 


I.   PYRIDINE,  C5H5N. 

387.  Pyridine  and  some  of  its  homologucs  are  constituents  of 
coal-tar.  On  mixing  the  "light  oil "  (286)  with  sulphuric  acid,  they 
are  absorbed  by  the  latter,  and  separate  on  addition  of  sodium  car- 
bonate in  the  form  of  a  dark-brown,  basic  oil,  from  which  pyridine 
and  its  homologues  are  obtained  by  fractional  distillation.  Pre- 
pared by  this  method,  pyridine  is  never  quite  pure,  always  con- 
taining small  proportions  of  its  homologues. 

Another  source  of  pyridine  is  "  DippeFs  oil,"  a  liquid  of  ex- 
tremely disagreeable  odour,  obtained  by  the  dry  distillation  of 
bones  which  have  not  been  deprived  of  their  fat.  It  is  a  very 
complicated  substance,  containing,  in  addition  to  the  pyridine 
bases  and  quinoline,  many  other  substances,  such  as  nitriles,  amines, 
and  hydrocarbons. 

Pyridine  is  a  colourless  liquid  boiling  at  115°,  and  with  a  specific 
gravity  of  1-0033  at  0°.  It  is  miscible  with  water  in  all  propor- 
tions, and  has  a  weak  alkaline  reaction,  colouring  aqueous  solutions 
of  litmus  only  purple.  It  has  a  very  characteristic  odour,  reminis- 
cent of  tobacco-smoke,  and  is  a  constituent  of  crude '  ammonia. 
It  is  very  stable,  being  unattacked  by  boiling  nitric  acid  or  chromic 
acid.  It  reacts  with  sulphuric  acid  only  at  high  temperatures, 
yielding  a  sulphonic  acid.  The  halogens  have  very  slight  action 
on  it.  On  very  energetic  reduction  with  hydriodic  acid  at  300°, 
it  yields  normal  pentane  and  ammonia. 

Being  a  base  it  forms  salts  with  acids,  mostly  readily  soluble 
in  water. 

Pyridine  ferrocyanide  dissolves  with  difficulty,  and  is  employed 
in  the  purification  of  the  base.     With  platinum  chloride,  the  hydro- 

554 


§  388]  PYRIDINE.  555 


chloride  yields  a  double  salt,  (CsHgN^EkPtCU,  freely  soluble  in 
water.  When  the  solution  is  boiled,  two  molecules  of  hydrochloric 
acid  are  eliminated,  with  production  of  a  yellow  compound, 
(C6H5N)2PtCl4,  which  is  only  slightly  soluble  in  water:  the  reaction 
affords  a  delicate  test  for  pyridine. 

The  following  test  is  also  very  delicate.  On  warming  the  base 
with  methyl  iodide,  an  energetic  reaction  takes  place,  with  forma- 
tion of  an  addition-product,  C5H5N  «CH3I.  When  warmed  with  solid 
potash,  this  compound  gives  off  a  very  pungent  and  disagreeable 
odour. 


Many  methods  for  the  synthesis  of  pyridine  and  its  homo- 
logues  are  known,  although  but  few  of  them  afford  insight  into  its 
constitution.  Among  them  is  the  formation  of  pyridine  from 
quinoline  (400)  ;  that  of  piperidine  from  pentamethylenediamine 
is  mentioned  in  159.  Piperidine  can  be  oxidized  to  pyridine  by 
heating  with  sulphuric  acid  : 

H 


yi2  —      jx  x» 

CH2<  >NH  ->  HC(     >  N. 

\CH2—  CH/  \C-CH 

Piperidine  JJ 

Pyridine 

The  formation  of  {3-chloropyridine  from  pyrrole  is  described  in 
395 

The  converse  of  these  syntheses  is  the  decomposition  of  piperi- 
dine,  discovered  by  VON  BRAUN.  On  treatment  of  behzoylpiperidine, 
C5H10N-COC0H5,  with  phosphorus  pentabromide,  PBr5,  the  oxygen 
is  replaced  by  two  bromine  atoms.  Distillation  converts  this 
dibromo-derivative  into  pentamethylene  dibromide  and  benzonitrile  : 

yCH2*CH2v  xCH2*CH2*Br 

CH2<;  >N  •  CBr2  •  C6H5  =  CH2<;  +  NC  •  C6H5. 

XCH2-CH/  XCH2-CH2.Br 

A  practical  method  is  thus  afforded  of  preparing  pentamethylene 
dibromide,  a  substance  of  importance  in  various  syntheses. 

Since  pyridine  is  reduced  to  piperidine  by  sodium  and  alco- 
hol, and  piperidine  can  be  oxidized  to  pyridine,  it  may  be  assumed 
that  pyridine  has  the  same  closed  chain  as  piperidine;  that  is,  one  of 
five  C-atoms  and  one  N-atom.  Moreover,  it  can  be  proved  that 


556  ORGANIC  CHEMISTRY.  [§338 

the  N-atom  in  pyridine  is  not  linked  to  hydrogen;  for,  while  piperi- 
dine  possesses  the  character  of  a  secondary  amine,  yielding  a  nitroso- 
derivative,  for  example,  pyridine  has  that  of  a  tertiary  amine;  thus, 
it  yields  an  addition-product  with  methyl  iodide  (387),  and  the 
iodine  atom  in  this  substance,  like  that  in  other  ammonium  iodides, 
can  be  exchanged  for  hydroxyl  by  means  of  moist  silver  oxide. 

The  number  of  isomeric  substitution-products,  like  that  of  ben- 
zene (282),  indicates  that  each  carbon  atom  is  in  union  with  one 
hydrogen  atom.  A  substance  of  the  formula 


or 


should  yield  three  monosubstitution-products,  2(a)=6(a'), 
3(/?)  =  5(/?'),  and  4(;-).  Moreover,  for  similar  substituents,  six 
disubstitution-products  are  possible:  2:3  =  6:5;  3:4  =  5:4; 
2:4  =  6:4;  2:6,  3:5,  and  2:5  =  6:3.  This  view  agrees  with  the 
results  of  experiment.  The  mode  of  linking  of  three  out  of  the 
four  valencies  of  each  carbon  atom  is  thus  established,  and  that  of 
two  of  the  three  nitrogen  valencies :  it  remains  only  to  determine 
how  the  fourth  valency  of  each  carbon  atom  and  the  third  valency 
of  the  nitrogen  atom  are  distributed  in  the  molecule. 

The  marked  analogy  between  benzene  and  pyridine  leads  to  the 
assumption  of  analogous  formulae  for  both  (283) .  The  great  stabil- 
ity of  pyridine  towards  energetic  chemical  reagents  proves  that  it 
does  not  possess  double  linkings.  Only  the  side-chains  of  both 
compounds  are  attacked  by  oxidizing  agents:  with  sulphuric  acid, 
both  yield  sulphonic  acids,  which  are  converted  by  fusion  with 
caustic  potash  into  hydroxyl-derivatives,  and  by  heating  with 
potassium  cyanide  into  cyanides.  At  330°,  pyridine  is  converted 
by  a  mixture  of  fuming  sulphuric  acid  and  nitric  acid  into  /?- 
nitropyridine,  colourless  needles  melting  at  41°,  and  boiling  at  216°. 
The  hydroxyl-derivatives  of  pyridine  have  a  phenolic  character: 
they  yield  characteristic  colorations  with  ferric  chloride.  Pyridine 
must,  therefore,  be  regarded  as  benzene  with  one  of  its  CH- 
groups  replaced  by  a  N-atom. 


§  389]  HOMOLOGUES  OF  PYRIDINE.  557 

The  principle  of  the  orientation  of  pyridine  is  the  same  as  that 
of  benzene — conversion  of  a  compound  of  unknown  structure  into 
one  with  its  side-chains  in  known  positions.  The  monocarboxylic 
acids  and  dicarboxylic  acids  have  served  as  the  main  basis  for  its 
orientation.  The  method  of  ascertaining  the  positions  occupied 
by  the  carboxyl-groups  in  these  compounds  is  described  in  391. 

Homologues  of  Pyridine. 

389.  The  homologues  of  pyridine  are  the  methylpyridines  or 
picolines,  dimethylpyridines  or  lutidines,  and  trimethylpyridines  or 
collidines.  Many  of  them  can  be  obtained  by  more  or  less  complex 
methods :  thus,  /?-picoline  is  formed  by  the  distillation  of  acralde- 
hyde-ammonia  (141),  and  collidine  by  the  distillation  of  crotonalde- 
hyde-ammonia.  The  formation  of  pyridine  and  its  homologues 
by  the  dry  distillation  of  bones  depends  upon  these  reactions: 
under  the  influence  of  heat,  the  fat  present  yields  acraldehyde, 
which  reacts  with  the  ammonia  resulting  from  the  "heating  of  the 
proteins,  forming  pyridine  bases. 

HANTZSCH  has  discovered  an  important  synthesis  of  pyridine 
derivatives— the  condensation  of  one  molecule  of  aldehyde-ammonia 
with  two  molecules  of  ethyl  acetoacetate : 

CH3 

OCH 
QjH50  •  OC  •  CH2          CH2  •  CO  •  OC2H5 

I  I 

CH3'CO  CO-CHa 

HNH2 

CH3 

/6H\ 

C2H5OOC-C  OCOOC2H5 

+  3H20. 
CH3C  C-CH3 

\N/ 

H 

Diethyl  dihydrocollidinedicarboxylate 

On  oxidation  with  nitrous  acid,  this  substance  loses  two  H-atoms, 
one  from  the  CH-group  and  one  from  the  NH-group,  with  forma- 
tion of  ethyl  collidinedicarboxylate.  On  saponification  with  caustic 


558  ORGANIC  CHEMISTRY.  [§390 

potash,  and  subsequent  heating  of  the  potassium  salt  with  quick- 
lime, the  carboxyl-groups  are  eliminated,  and  collidine, 

CH, 


N 
distils. 

In  this  synthesis  acetaldehyde  may  be  replaced  by  other  alde- 
hydes, and  ethyl  acetoacetate  by  the  esters  of  other  /?-ketonic  acids, 
so  that  it  affords  a  method  of  preparing  numerous  pyridine  deriva- 
tives. 

Some  of  the  homologues  of  pyridine  can  be  obtained  from 
it  by  the  action  of  an  alkyl  iodide,  an  addition-product  being 
formed.  On  heating  this  compound  to  300°,  the  alkyl -group  be- 
comes detached  from  the  nitrogen  atom  and  linked  to  a  carbon 
atom,  a  reaction  analogous  to  the  formation  of  p-toluidine  by 
heating  methylaniline  hydrochloride  to  a  high  temperature  (299) . 

390.  a-Propenylpyridine  is  of  theoretical  importance.  LADEN- 
BURG  obtained  it  by  the  condensation  of  a-picoline  with  acetalde- 
hyde: 

NC5H4  •  CH3  +  OCH  •  CH3  =  NC5H4  •  CH :  CH .  CH3  +  H20. 

o-Picoline  Acetaldehyde  a-Propenylpyridine 

By  its  aid  he  effected  the  first  synthesis  of  a  natural  alkaloid,  that 
of  conii'ne,  CgH^N  (409).  a -Propenylpyridine  was  reduced  with 
sodium  and  boiling  alcohol,  yielding  a-propylpiperidine, 


H 


optically  inactive,  like  all  synthetical  substances  prepared  from 
inactive  material.  This  substance  was  resolved  into  a  dextro- 
rotatory and  a  Isevo-rotatory  modification  by  fractional  crystal- 
lization of  its  tartrate,  the  dextro-rotatory  isomeride  being 
named  isoconime  because  heating  at  300°  transforms  it  into  an 
isomeride  identical  with  natural  conime.  LADENBURG  attributes 
the  difference  between  conime  and  isoconiine  to  asymmetry  of 
the  nitrogen  atom. 


§  391]  PYRIDINECARBOXYLIC  ACIDS.  559 

The  constitutional  formula  of  a-propylpiperidine  indicates  that 
the  carbon  atom  in  union  with  the  propyl-group  is  asymmetric. 
?--Propylpiperidine  does  not  contain  an  asymmetric  carbon  atom, 
and  should  therefore  be  optically  inactive.  The  side-chain  cannot 
be  at  the  /3-position,  for  coniine  yields  ammonia  and  normal 
octane  when  strongly  heated  with  hydriodic  acid.  Thus  treated,  a 
/9-propylpiperidine  or  ^-propylpiperidine  must  yield  an  octane  with 
a  branched  carbon-chain,  which  proves  that  coniine  is  an  a-com- 
pound. 

Piperidine  is  present  in  pepper  in  combination  as  pipeline, 
CnHigOsX.  On  boiling  with  alkalis,  it  yields  piperic  acid  (353), 
Ci2Hi004,  and  piperidine,  by  addition  of  one  molecule  of  water. 
Piperine  must,  therefore,  be  a  substituted  amide  of  piperic  acid, 
containing  the  piperidine-residue,  C5Hi0N  —  ,  instead  of  the  NH2- 
group: 


H2C 


Piperine 


Piperidine  is  a  colourless  liquid,  boiling  at  106°,  with  a  charac- 
teristic pepper-like  odour  and  strongly-marked  basic  properties  (159). 
It  is  best  obtained  by  the  electro-reduction  of  pyridine. 


Pyridinecarboxylic  Acids. 
391.  Three  pyridinemonocarboxylic  acids  are  known. 

N 

COOH 


r> 
)H 

Picolinic  acid  (a)  Nicotinic  acid  (.3)  isoNicotinic  acid  (;•) 

The  orientation  of  the  carboxyl-groups  in  these  acids  can  be  carried 
out  as  follows.  It  is  stated  in  390  that  the  side-chain  in  coniine 
occupies  the  ct-position.  On  oxidation,  this  substance  yields  pico- 


560  ORGANIC  CHEMISTRY.  [§  391 

linic  acid,  by  conversion  of  the  propyl-group  into  a  carboxyl-group, 
and  elimination  of  the  six  added  hydrogen  atoms.  Picolinic  acid 
is  therefore  the  a-carboxylic  acid. 

Nicotinic  acid  is  proved  to  have  the  ^-constitution  thus.    Quino- 
line  (400)  has  the  formula 


It  is  naphthalene  with  one  of  the  a-CH-groups  replaced  by  N.  On 
oxidation,  quinoline  yields  a  pyridinedicarboxylic  acid,  quinolinfc 
acid,  which  must  therefore  have  the  structure 


eicooH 


On  heating  this  acid,  one  molecule  of  carbon  dioxide  is  eliminated, 
with  formation  of  nicotinic  acid.  Since  the  carboxyl-group  in 
picolinic  acid  has  been  proved  to  occupy  the  a-position,  nicotinic 
acid  must  be  the  /?-acid.  There  remains  only  the  ^-structure  for 
isonicotinic  acid. 

The  pyridinemonocarboxylic  acids  are  formed  by  the  oxidation 
of  the  homologues  of  pyridine  containing  a  side-chain.  Nicotinic 
acid  derives  its  name  from  its  formation  by  the  oxidation  of  nico- 
tine. The  monocarboxylic  acids  are  crystalline,  and  possess  both 
a  basic  and  an  acidic  character.  As  bases,  they  yield  salts  with 
acids,  and  double  salts  with  platinum  chloride  and  mercuric  chloride, 
etc.  As  acids,  they  form  salts  with  bases,  the  copper  salts  being 
often  employed  in  their  separation. 

Picolinic  acid  can  be  distinguished  from  its  isomerides  by  two 
properties :  on  heating,  it  loses  CO2  more  readily,  with  formation  of 
pyridine;  and  it  gives  a  yellowish-red  coloration  with  ferrous 
sulphate.  Quinolinic  acid  answers  to  the  same  tests:  it  may,  there- 
fore, be  concluded  that  they  are  applicable  to  acids  with  a  carboxyl- 
group  in  the  a-position. 


§  392]  FURAN.  561 

II.  [FURAN,*  C4H40. 

392.  Furan,  C4H40,  B.P.  36°,  is  of  little  importance,  but  two 
of  its  substitution-products  must  be  considered  in  some  detail. 
To  furan  is  assigned  the  ring-formula 

O  O  O 


HC     CH 

ll       II 
HC — CH 


r  i 

'5     2 


or 


or 


This  formula  is  supported  by  the  resemblance  in  properties  between 
some  of  its  derivatives,  such  as  furfuraldehyde  (furfural  or  furfurole)> 

TT 

C4H30'CQ,  and  the  corresponding  benzene  derivatives.  More- 
over, the  0-atom  can  be  proved  to  be  linked  similarly  to  that  of 
ethylene  oxide  (150),  for  on  treatment  with  sodium,  furan  does  not 
evolve  hydrogen,  proving  the  absence  of  a  hydroxyl-group ;  and  it 
does  not  react  with  hydroxylamine  or  phenylhydrazine,  indicating 
that  it  has  no  carbonyl-group. 

Furan  derivatives  can  be  obtained  from  the  1 : 4-diketones,, 
R»CO.CH2-CH2-CO.R,  by  treatment  with  dehydrating  agents, 
such  as  acetyl  chloride.  This  reaction  may  be  regarded  as  the 
result  of  the  conversion  of  the  diketone  into  an  unstable,  tauto- 
meric  form,  R.C:CH-CH:C-R,  which  loses  water: 

OH  OH 


NO.TT  HC=C<f 

^-H20  =        |          > 

OH  HG=C< 

\E  XR 


*  The  CHEMICAL  SOCIETY  OF  LONDON  adopts  the  name  furan  for  the 
O 
/\ 

simple  ring  f      ] ,  the  corresponding  radical  being  furyl.     The  double  syl- 


lable furfur  ...  is  reserved  for  derivatives  with  a  side-chain,  containing  the 
ring  f         C\. 


562 


ORGANIC  CHEMISTRY. 


[§  393 


This  method  yields  2:5-furan  derivatives,  the  C-atoms  in  furan 
being  denoted  as  in  the  scheme  previously  indicated. 

This  synthesis  of  furan  derivatives  is  likewise  a  proof  of  their 
constitution. 

393.  The  most  important  derivatives  of  furan  are  furfuralde- 
%cfe  C4H30'CQ,  and  pyromucic  acid,  C4H3O-COOH:  both  have 
long  been  known. 

Furfuraldchyde  is  prepared  from  pentoses  by  the  method  men- 
tioned in  207.  It  has  the  character  of  an  aromatic  aldehyde: 
like  benzaldehyde  (314),  it  is  converted  by  alcoholic  potash  into  the 
corresponding  acid,  pyromucic  acid,  and  the  corresponding  alcohol, 
furfuryl  alcohol,  C4H30-CH2OH: 


R       —  » 

4- 

u 

co 

XX 

COOH 

\/ 

CH2OH. 

o                  o                     6 

Furfuraldehyde                  Pyromucic  acid                    Furfuryl  alcohol 

With  ammonia  it  yields  fur  fur  amide,  (CgHtO^Naj  analogous  in 
composition  to  hydrobenzamide  (315).  Just  as  benzaldehyde  con- 
denses in  presence  of  potassium  cyanide  to  benzoin  (376),  furfur- 
aldehyde  under  the  same  conditions  yields  the  similarly  constituted 
H 

furfurom,  C4H3O'C-CO'C4H3O.    The  resemblance  in  properties 

OH 
between  the  two  compounds  is,  therefore,  very  striking. 

Furfuraldehyde  is  proved  to  have  the  2-structure  by  various 
means:  for  example,  by  its  formation  from  pentoses  (207),  a  reac- 
tion which  may  be  represented  by  the  scheme: 


HO     H 
I        I 


CH-CHOJH 
CH-C— OH 




CH=CH 


Pentose 


o 

Furfuraldehyde 


§  393]  FURFURALDEHYDE.  563 

Furfuraldehyde  thus  results  from  the  elimination  of  three  molecules 
of  water  under  the  influence  of  hydrochloric  acid  or  sulphuric  acid. 
It  is  a  colourless,  oily  liquid  of  agreeable  colour,  and  boils  at  162°. 
A  test  for  it  is  described  in  207. 

Analogous  to  the  conversion  of  pentoses  into  furfuraldehyde  is 
that  of  ketohexoses  into  hydroxymethylfurfuraldehyde, 

HC — CH 

II       II 
HO-CH2-C 


O 

effected  by  heating  with  dilute  acids.  The  structure  of  this  sub- 
stance is  proved  by  its  oxidation  to  the  dibasic  dehydromucic  acid, 

HC — CH 
HOOC-C      C-COOH. 

V 

o 

Heating  with  hydrochloric  acid  or  dilute  sulphuric  acid  converts 
hydroxymethylfurfuraldehyde  almost  quantitatively  into  formic 
acid  and  Isevulic  acid: 

C6H603+2H20  =H-COOH+C5H803. 

Hydroxymethyl-  Laevulic 

'    furfuraldehyde  acid 

The  formation  of  hydroxymethylfurfuraldehyde  is  the  cause  of 
certain  reactions  exhibited  by  the  hexoses.  When  heated  with 
resorcinol  and  concentrated  hydrochloric  acid,  it  yields  a  dark-red 
precipitate.  This  reaction  serves  to  distinguish  the  artificial  honey 
made  from  invert-sugar  (209)  from  the  natural  product,  since  in 
the  inversion  of  the  sucrose  by  heating  with  dilute  acid  a  small 
proportion  of  hydroxymethylfurfuraldehyde  is  formed. 

As  its  name  indicates,  pyromucic  acid  is  formed  by  the  dry  dis- 
tillation of  mucic  acid  (211).  It  can  also  be  obtained  by  oxidiz- 
ing furfuraldehyde  with  silver  oxide.  It  is  crystalline,  melts  at  132°, 
can  be  readily  sublimed,  and  dissolves  freely  in  hot  water.  When 
heated  at  275°  in  a  sealed  tube,  it  yields  carbon  dioxide  and  furan. 


564  ORGANIC  CHEMISTRY.  [§  394 

Pyromucic  acid  wholly  lacks  the  character  of  an  aromatic  com- 
pound: its  properties  in  no  way  resemble  those  of  benzoi'c  acid,  but 
are  like  those  of  the  unsaturated  aliphatic  acids.  Thus,  it  easily 
undergoes  oxidation:  it  almost  instantaneously  decolorizes  VON 
BAEYER'S  reagent  (113),  and  readily  adds  four  bromine  atoms. 
Hence,  the  distinguishing  characteristics  of  the  benzene-nucleus  are 
absent,  so  that  the  formula 

HC=CH 
>0 


~v  J 

COOH 


with  two  double  bonds,  must  be  assigned  to  it. 


III.     PYRROLE,  C4H5N. 

394.  Pyrrole  is  the  most  important  of  the  heterocyclic  com- 
pounds with  a  ring  of  five  atoms.  Several  natural  products  con- 
taining the  pyrrole-nucleus  are  known:  examples  are  the  colouring- 
matter  of  blood;  chlorophyll;  and  certain  alkaloids,  among  them 
nicotine.  Pyrrole  derivatives  have  also  been  found  among  the 
decomposition-products  of  proteins.  Pyrrole  is  a  constituent  of 
"  Dippel's  oil"  (387).  The  fraction  of  this  oil  which  distils  between 
120°  and  130°  is  employed  in  the  preparation  of  pyrrole.  After 
removal  of  the  pyridine  bases  by  treatment  with  dilute  sulphuric 
acid,  and  of  the  nitriles  by  boiling  with  sodium  carbonate,  the  frac- 
tion is  dried,  and  treated  with  potassium.  Potassiopyrrole,  C^I^NK, 
is  formed,  and  can  be  purified  by  washing  with  ether.  It  is  recon- 
verted into  pyrrole  by  the  action  of  water. 

Pyrrole  is  a  colourless  liquid,  specifically  somewhat  lighter  than 
\vater,  and  boiling  at  131°.  On  exposure  to  light,  it  soon  acquire? 
a  brown  colour.  The  vapours  of  pyrrole  and  its  derivatives  impart 
a  carmine-red  colour  to  a  wood-shaving  moistened  with  hydro- 
chloric acid,  due  to  the  formation  of  an  amorphous  substance, 
"pyrrole-red."  This  reaction  furnishes  a  delicate  test  for  pyrrole 
and  its  derivatives. 

Pyrrole  can  be  synthesized  by  several  methods:  for  example, 
by  the  interaction  of  succindialdehyde  and  ammonia: 


§  395]  PYRROLE.  565 

CH2— c5  +  NH3       CH2— CH 

I  =   I 

CH2— C^  +  N  H3       CH2— CH 

CH=€H> 
=  CH=C 

Pyrrole 

Inversely,  succinald-dioxime  is  obtained  from  pyrrole  by  the 
action  of  hydroxylamine,  ammonia  being  evolved. 

The  homologues  of  pyrrole  are  produced  by  the  interaction 
of  ammonia  and  l:4-diketones: 


s 

HC=:C 


NH  +  2H20. 


1  :  4-Diketone  aa'-Pyrrole 

(tautomeric  form) 

The  nomenclature  of  the  pyrrole  derivatives  is  indicated  in  the 
scheme 

NH  NH 


or 


a'. 


This  structure  is  inferred  from  the  foregoing  syntheses  and  other- 
wise. The  basic  properties  which  should  be  characteristic  of  a 
substance  with  the  formula  of  pyrrole  are  masked  by  the  resinifying 
action  of  acids.  As  a  result  of  this  influence,  no  sulpho-acids  have 
been  obtained,  and  nitro-derivatives  only  by  an  indirect  method. 

395.  Among  the  properties  of  pyrrole  indicating  its  relation  to 
the  aromatic  compounds  is  its  behaviour  with  halogens:  unlike  an 
aliphatic  unsaturated  compound,  it  yields  substitution-products, 
but  not  addition-products.  The  analogy  in  properties  between 
pyrrole  and  aniline,  and  especially  phenol,  is  very  marked.  The 
transformation  of  1-methylpyrrole  into  2-methylpyrrole  under 
the  influence  of  heat  resembles  the  conversion  of  methylaniline 
into  p-toluidine  (299) : 

C4H4N.CH,  ->  CiH3(CH3)  •  NH. 

l-Methylpyrrole  2-Methylpyrrole 

Just  as  sodium   phenoxide  is   converted   by  carbon  dioxide  into 


566  ORGANIC  CHEMISTRY.  [§396 

salicylic  acid  (344),  so  potassiopyrrole  and  carbon  dioxide  yield 
2-pyrrolecarboxylic  acid.  Like  phenol,  pyrrole  unites  with  ben- 
zenediazonium  chloride,  with  elimination  of  hydrochloric  acid  (309) . 
When  pyrrole  is  treated  with  chloroform  in  presence  of  sodium 
alkoxide,  a  notable  reaction  ensues.  The  C-atom  of  the  chloroform 
takes  up  a  position  between  two  of  the  C-atoms  of  the  pyrrole- 
nucleus,  forming  ft-chloropyridine: 

NH  N 

CHCl 


Pyrrole  /?-Chloropyridine 

On  reduction  with  zinc-dust  and  cold  hydrochloric  acid,  pyrrole 
takes  up  two  hydrogen  atoms,  forming  2 '•'^-dihydropyrrole^' 
C^IyN,  which  boils  at  91°.  Like  the  partial  reduction-products  of 
aromatic  compounds,  dihydropyrrole  behaves  as  an  unsaturated 
compound,  another  indication  of  the  aromatic  character  of  pyrrole. 

IV.   THIOPHEN,   C4H4S. 

396.  Thiophen  has  a  more  aromatic  character  than  furan  or  pyr- 
role. It  is  present  in  the  crude  benzene  obtained  from  coal-tar  (286) 
to  the  extent  of  about  0-5  per  cent.:  its  homologues,  thiotolen  or 
methylthiophen,  and  thioxen  or  dimethylthiophen,  are  contained  in 
toluene  and  xylene  from  the  same  source. 

Thiophen  was  first  obtained  by  VICTOR  MEYER  by  agitating 
coal-tar  benzene  with  small  amounts  of  concentrated  sulphuric 
acid  till  it  ceased  to  give  the  indophenin-reaction,  a  blue  coloration 
with  isatin  (403)  and  concentrated  sulphuric  acid.  By  this  treat- 
ment the  thiophen  is  converted  into  a  sulphonic  acid,  from  which 
it  can  be  regenerated  by  the  action  of  superheated  steam. 

A  better  method  for  the  separation  of  benzene  and  thiophen 
is  to  boil  the  crude  benzene  with  mercuric  oxide  and  acetic  acid. 
The  thiophen  is  precipitated  as  thiophen  mercury  oxyacetate, 
C<H2S(HgOOC-CH3)-HgOH,  which  is  reconverted  into  thiophen  by 
distillation  with  moderately  concentrated  hydrochloric  acid.  It  is 
formed  by  passing  acetylene  over  pyrites  at  300°. 

*  The  CHEMICAL  SOCIETY  OF  LONDON  employs  the  name  dihydropyrrole 
for  the  compound  C4H7N,  and  tetrahydropyrrole  for  C4H9N.  In  the  nomen- 
clature of  the  GERMAN  CHEMICAL  SOCIETY  the  corresponding  terms  are 
pyrrolin  and  pyrrolidin. 


§  396]  THIOPHEN.  567 

Thiophen  can  be  synthesized  by  various  methods,  the  most 
important  being  the  interaction  of  succinic  acid  and  phosphorus 
pentasulphide.  On  heating  a  mixture  of  these  substances,  a  vigor- 
ous reaction  ensues,  carbon  disulphide  is  evolved,  and  a  liquid,  con- 
sisting chiefly  of  thiophen,  distils. 

It  is  a  colourless  liquid,  boiling  at  84°,  a  temperature  which 
differs  little  from  the  boiling-point  of  benzene  (80-4°),  It  has  a 
faint,  non-characteristic  odour.  It  is  heavier  than  water,  its  specific 
gravity  being  1-062  at  23°. 

Bromine  reacts  energetically  with  thiophen,  forming  chiefly 
dibromothiophen,  C4H2Br2S,  along  with  a  small  proportion  of  the 
monobro  mo-derivative. 

The  notation  of  thiophen  derivatives  is  indicated  by  the  schemes 

S  S 

and 


The  homologues  of  thiophen  can  be  obtained  by  FITTIG'S  syn- 
thesis (287)  and  by  other  methods:  for  instance,  by  heating  1:4- 
diketones  with  phosphorus  pentasulphide,  a  mode  of  synthesis 
which  proves  the  constitution  of  the  thiophen  homologues.  Thus, 
acetonylacetone  yields  dimethylthiophen  : 


HC=C 

OH 


H 
— 

\CH 


Acetonylacetone          2  :5-Dimethylthiophen 
(tautomeric  form) 

2:5-Dialkylthiophens  are  obtained  from  1  :  4-diketones  :  the 
3:4-alkyl-compounds  can  be  prepared  by  another  method.  As 
stated,  thiophen  results  from  the  interaction  of  succinic  acid  and 
phosphorus  pentasulphide: 

H 
H2C—  COOH  HO=CX 

I  ->        I       V 

H2C—  COOH  HC=(X 

H 

Succinic  acid  Thiophen 


568  ORGANIC   CHEMISTRY.  [§397 

Similarly,  a  monoalkylsuccinic  and  symmetrical  dialkylsuccinic 
acid  respectively  yield  a  3-alkylthiophen  and  a  3 :4-alkylthiophen: 

CH3-CH— COOH  CH3.C— CH 

I  ->  I       >S. 

CH3.CH-COOH  CH3.C-CH 

Symmetrical  dimethyl-  3 : 4-Dimethyl- 

succinic  acid  thiophen 

The  known  structure  of  these  compounds  can  be  employed  as 
a  basis  for  the  orientation  of  the  derivatives  of  thiophen. 

397.  When  a  cold  aqueous  solution  of  the  two  monocarboxylic 
acids,  2-thiophencarboxylic  acid  and  3-thiophencarboxylic  acid, 

S  S 


/NCOOH    and     /\ 
- 


is  crystallized  slowly,  there  is  formed  a  mixture  which  cannot  be 
resolved  into  its  components.  This  phenomenon  is  due  to  the 
formation  of  mixed  crystals,  and  is  of  rare  occurrence  with  posi- 
tion-isomerides.  On  oxidizing  a  mixture  of  2-thiotolen  and  3- 
thiotolen,  an  apparently  homogeneous  acid  is  obtained:  from  its 
method  of  formation,  however,  it  can  only  be  a  mixture  of  the 
corresponding  acids. 

A  thiophensulphonic  acid  is  also  known :  it  is  more  easily  formed 
than  benzenesulphonic  acid,  which  is  the  basis  of  VICTOR  MEYER'S 
method  of  separating  thiophen  and  benzene. 

When  a  mixture  of  acetic  anhydride  and  concentrated  nitric 
acid  is  added  to  thiophen,  mononitrothiophen  is  formed.  It 
is  a  solid,  melting  at  44°,  and  boiling  at  224°:  it  has  an  odour 
like  that  of  nitrobenzene.  On  reduction,  it  yields  aminothiophen, 
or  thiophenine,  which  differs  from  aniline  in  being  very  unstable: 
it  changes  quickly  to  a  varnish-like  mass,  but  its  hydrochloride 
is  stable.  It  does  not  yield  diazo-compounds,  but  reacts  with 
benzenediazonium  chloride,  forming  a  crystalline,  orange  dye. 

V.   PYRAZOLE,  C3H4N2. 

398.  Pyrazole  derivatives  are  produced  by  the  interaction  of  the 
esters  of  unsaturated  acids  and  ethyl  diazoacetate.  An  exampla 
is  the  union  with  explosive  energy  of  diethyl  acetylenedicar- 


398] 


PYRAZOLE. 


569 


boxylate    and   ethyl    diazoacetate    to   form    triethyl    pyrazoletri- 
carboxylate  : 

CH.COOC2H5    C2H5OOC.C  -  C.COOC2H5 

II      I' 

=  C2H5OOC.C      N 

\/ 
Nil 

Triethyl  pyrazoletricarboxylate 


C2H5OOC.C+ 


N 


Diethyl  acetylene- 
dicarboxylate 


Pyrazole  is  formed  in  several  reactions,   one  of  them  being 
the  combination  of  hydrazine  with  propiolaldehydeacetal  (142)  : 

CH=C.CH(OC2H5)2  +  H2 

Propiolaldehydeacetal 


Intermediate  product 
(not  isolated) 


C— CH 

[IIH> 
OH   / 

NH2 

Intermediate 
product 


CH— CH 

k  > 

\NH 

Pyrazole 


Nil 


or 


/l\ 


N. 


This  synthesis  proves  that  pyrazole  has  the  formula  indicated, 
so  that  it  may  be  regarded  as  pyrrole  in  which  one  of  the  CH-groups 
has  been  replaced  by  N. 

It  is  crystalline,  melts  at  70°,  and  is  very  stable.  It  is  only  a 
weak  base,  for  its  aqueous  solution  has  a  neutral  reaction. 


The  identity  of  the  3-derivatives  and  the  5-derivatives  of 
pyrazole  is  of  theoretical  interest,  since  the  structural  formula 
given  indicates  that  they  should  be  dissimilar.  On  replacing  the 
hydrogen  atom  of  the  imino-group  by  alkyl  or  phenyl,  the  deriv- 
atives with  substituents  at  positions  3  and  5  are  no  longer  identical. 
Since  migration  of  the  hydrogen  atom  from  one  nitrogen  atom  to 
the  other,  with  a  simultaneous  migration  of  the  double  bonds,  makes 
position  3  equivalent  to  position  5,  it  must  be  assumed  that  free 
pyrazole  readily  undergoes  this  type  of  tautomerization : 

NH  N 


570  ORGANIC  CHEMISTRY.  [§399 

399.  The  derivatives  of  pyrazole  are  not  important,  but  there 
are  valuable  products  related  to  its  dihydride,  pyrazoline,  C3H6N2. 
Substances  of  this  type  are  prepared  by  condensing  ethyl  diazo- 
acetate  with  esters  containing  a  double  linking: 

C2H5OOC  •  CH     GH  -  COOC2H5    C2H5OOC  •  CH— C  •  COOC2H5 

C2H5OOC.CH+  L>N  =  C2H5OOC.CH     N 

N  V 

NH 

Diethyl  fumarate  Triethyl  pyrazolinetricarboxylate 

Pyrazoline  (I.)  is  formed  by  the  interaction  of  hydrazine 
hydrate  and  acraldehyde.  Bromine  converts  it  into  pyrazole. 
Pyrazolone  (II.)  is  a  ketonic  derivative  of  pyrazoline: 

NH  NH 

H2C     N  OC    N 

H2C — CH  H2C — CH 

i.  u. 

Substitution-products  of  pyrazolone  are  obtained  by  the  interac- 
tion of  ethyl  acetoacetate  and  phenylhydrazine : 


CH3— C|O  H2]N  CH3-C=N, 

H2C— CO  •  |OC2H5      H|NC6H5 


C[0 H2JJN  CH3-C=N 

_±_  -»  >N-C6H5. 

C— CO  •  [OC2H5      SNCeHs  H2C— CCT 


Meihylphenylpyrazolone  is  thus  formed.  Methylphenylhydrazine, 
CeHs'NH'NH-CHs,  condenses  similarly  with  ethyl  acetoacetate, 
yielding  a  dimethylphenylpyrazolone  of  the  formula 


CH3-C—  N(CH3) 
H 


||     >N.C6H5. 
C—  CO 


This  substance  is  called  "  antipyrine,"  and  was  discovered  by 
KNORR;  it  is  extensively  employed  in  medicine  as  a  febrifuge.     It 


399] 


PYRAZOLINE  DERIVATIVES. 


571 


crystallizes  in  white  leaflets  melting  at  113°.  It  cannot  be  dis- 
tilled without  undergoing  decomposition.  It  is  readily  soluble 
in  water  and  alcohol:  the  aqueous  solution  gives  a  red  coloration 
with  ferric  chloride,  and  a  bluish-green  coloration  with  nitrous 
acid. 

"  Salipyrine  "  is  a  compound  of  antipyrine  and  salicylic  acid. 


(CONDENSATION-PRODUCTS  OF  BENZENE  AND 
HETEROCYCLIC  NUCLEI. 

I.  QUINOLINE,  C9H7N. 

400.  Quinoline  is  present  in  coal-tar  and  bone-oil, but  is  difficult 
to  obtain  pure  from  these  sources.  It  is  prepared  by  SKRAUP'S 
synthesis,  described  below.  It  is  a  colourless,  highly  refractive 
liquid  of  characteristic  odour:  it  boils  at  236°,  and  has  a  specific 
gravity  of  1  •  1081  at  0°.  It  has  the  character  of  a  tertiary  base,  so 
that  it  possesses  no  hydrogen  linked  to  nitrogen.  It  yields  salts 
with  acids:  the  dichromate,  (CgHyN^H^C^Oy,  dissolves  with  diffi- 
culty in  water . 

Quinoline  can  be  synthesized  by  various  methods  which  prove 
its  constitution.  Its  synthesis  was  first  effected  by  KONIGS,  by 
passing  allylaniline- vapour  over  red-hot  oxide  of  lead: 

H      NH  H 

J        IH    IpR2  +  20  = 
\  /     /^  '•'** 

H      CH2  H      H 

Allylaniline 

SKRAUP'S  synthesis  consists  in  heating  together  aniline,  glycerolr 
sulphuric  acid,  and  nitrobenzene.  In  presence  of  sulphuric  acid  as  a 
dehydrating  agent,  the  glycerol  loses  water,  forming  acraldehyde, 
which  unites  with  the  aniline  to  an  addition-product, 


In  KONIG'S  synthesis  the  oxidizing  agent  is  the  lead  oxide;  in  this 
reaction  it  is  the  nitrobenzene,  which  is  reduced  to  aniline.  Arsenic 
acid  can  be  substituted  for  nitrobenzene. 

VON  BAEYER  and  DREWSEN  have  discovered  another  method  of 
synthesis  which  proves  the  constitution  of  quinoline:   it  involves 

572 


§  401]  QUINOLINE.  573 

the  reduction  of  o-nitrocinnamaldehyde.  This  compound  is  first 
converted  into  an  intermediate  product,  the  corresponding  amino- 
derivative,  the  H-atoms  of  the  NH2-group  of  this  substance  being 
subsequently  eliminated  along  with  the  0-atom  of  the  aldehyde^ 
group: 


H 


H  H      H 

o-Aminocinnamaldehyde  Quinoline 

The  last  synthesis  proves  quinoline  to  be  an  orZ/io-substituted 
benzene:  the  constitution  of  the  ring  containing  the  N-atom  has 
now  to  be  determined.  The  method  employed  is  based  upon  oxi- 
dation, which  produces  a  dibasic  acid,  quinolinic  acid, 


On  distillation  with  quicklime,  quinolinic  acid  yields  pyridine. 
From  these  facts  it  must  be  concluded  that  quinoline  contains  a 
benzene-nucleus  and  a  pyridine-nucleus,  with  two  or^o-C-atoms 
common  to  both.  It  may  be  regarded  as  naphthalene,  with  one  of 
the  CH-groups,  1-4-5-8,  replaced  by  N. 

The  number  of  isomeric  substitution-products  is  very  large. 
The  seven  hydrogen  atoms  occupy  dissimilar  positions  relative  to 
the  nitrogen  atom,  and  consequently  seven  monosubstitution- 
products  are  possible.  Twenty-one  disubstitution-products  are 
possible  for  similar  substituents,  while  the  number  of  tri-derivatives 
possible  is  much  greater,  and  so  on. 

401.  There  are  three  methods  for  the  orientation  of  quinoline 
derivatives. 

First,  the  relative  method  (354,  1) . 

Second,  oxidation.  This  process  usually  removes  the  benzene- 
nucleus,  leaving  the  pyridine-nucleus  intact,  and  thus  furnishes 
a  means  of  determining  which  substituents  are  present  in 
each. 


574  ORGANIC  CHEMISTRY.  t§  401 

Third,  SKRAUP'S  synthesis— an  important  aid  to  orientation. 
It  can  be  carried  out  not  only  with  aniline,  but  with  many  of  its 
substitution-products,  such  as  homologues  of  aniline,  nitroanilines, 
aminophenols,  and  other  derivatives.  The  quinoline  compounds 
thus  obtained  have  their  substituents  in  the  benzene-nucleus.  But 
this  synthesis  also  indicates  the  positions  of  the  side-chains  when 
an  0r£/&o-substituted  or  a  para-substituted  aniline  is  used:  thus, 

X     ,NH2  X     N 


can  only  yield  ,       ,       , , 

Ortho 

NH2  N 

and    vf  only        v 

X      / 

Para 

NH  N 

while  X|       ]  can  yield  X|       I       ]    or 

V  \A/ 

Meta 


All  four  possible  quinoline  derivatives  with  substituents  in  the 
benzene-nucleus  can,  therefore,  be  prepared  by  SKRAUP'S  syn- 
thesis. 

The  nomenclature  of  the  quinoline  derivatives  is  indicated  in 
the  scheme 


Many  of  the  known  quinoline  derivatives  are  obtained  by 
SKRAUP'S  method,  a  smaller  number  directly  from  quinoline.  The 
sulphonic  acids  are  best  prepared  by  the  latter  method.  On  fusion 
with  caustic  potash,  they  are  converted  into  hydroxyquinolines; 
when  heated  with  potassium  cyanide,  they  yield  cyanoquinolines, 
which  on  hydrolysis  give  carboxylic  acids. 


§§  402,403]  isoQU  INCLINE  AND  INDOLE.  575 

Carbostyril,  or  2-hydroxyquinoline,  can  be  synthesized  by  the 
elimination  of  water  from  o-aminocinnamic  acid  : 

.  _  .  N 

yN|H70]C.OH  / 

C6H4  J|          -H20  = 


o-Aminocinnam!c  acid  Carbostyril 

It  has  a  phenolic  character:  thus,  it  dissolves  in  alkalis,  and  is 
reprecipitated  by  carbon  dioxide. 


II.  isoQUINOLINE,  C9H7N. 

402.  isoQuinoline  is  present  in  coal-tar,  from  which  HOOGEWERFF 
and  VAN  DORP  isolated  it  in  the  form  of  its  sparingly  soluble  sulphate. 
It  is  a  colourless  substance  with  an  odour  like  that  of  quinoline.  It 
melts  at  21°,  and  boils  at  237°.  It  has  the  formula 


tsoQuinoline 


f  This  constitution  is  indicated  by  its  oxidation  to  cinchomeronic  add 
and  phthalic  acid,  in  accordance  with  the  scheme 


N  _  . 

HOOC-'  ' 

Cinchomeronic  acid  Phthalic  acid 


The  synthesis  of  isoquinoline  furnishes  additional  confirmation  of 
the  structure  indicated. 


m.  INDOLE,  C8H7N. 

403.  The  relation  between  indigo  and  indole  is  made  evident 
by  the  following  series  of  transformations,  chiefly  the  discoveries 
of  VON  BAEYER. 

On  treatment  with  nitric  acid,  indigo,  CieHioC^^,  yields  an 


576  ORGANIC  CHEMISTRY.  [§  403 

oxidation-product,  isatin,  C8H5O2N,  which  can  also  be  synthe- 
sized by  treating  o-nitrobenzoyl  chloride  with  silver  cyanide. 
When  hydrolyzed,  the  resulting  nitrile  yields  o-nitrobenzoyl- 
formic  acid: 


p     TT      ^NO2  1  p     TT      ^NO2  p     T;         ^N02 

XJO-C12       U6±l4<CO.CN~   UU4<CO.COOH. 

jO-Nitrobenzoyl  g     o-Nitrobenzoyl  o-Nitrobenzoyl- 

chloride  cyanide  formic  acid 

On  reduction,  the  nitro-group  in  this  acid  is  converted  into  an 
amino-group,  and  water  eliminated  simultaneously  with  the  for- 
mation of  isatin,  which  has,  therefore,  the  constitution  indicated 
by  the  equation 


o-Aminobenzoylformic  acid  Isatin 


When  reduced  with  zinc-dust  and  hydrochloric  acid,  isatin  takes  up 
two  hydrogen  atoms,  forming  dioxindole,  C8H7O2N.  This  com- 
pound also  results  on  the  elimination  of  water  from  the  unstable 
o-aminomandelic  acid,  which  determines  its  constitution: 


o-Aminomandebc  acid 

OH 

Dioxindole 

When  reduced  with  tin  and  hydrochloric  acid,  dioxindole  yields 
oxindole,  CsH7ON,  which  is  also  obtained  by  reduction  of  o-nitro- 
phenylacetic  acid  and  subsequent  elimination  of  water: 


o-Aminophenylacetic  acid  Oxindole 

Distillation  with  zinc-dust  converts  oxindole  into  indole, 

XNH 
which  must,  therefore,  have  the  structure  CeH^ 


§  403]  INDOLE.  '  577 


Indole,  therefore,  possesses  a  benzene-nucleus  condensed  with  a 
pyrrole-nucleus.  It  does,  in  fact,  display  some  of  the  properties 
characteristic  of  pyrrole:  thus,  it  is  a  very  weak  base,  and  gives  a 
red  coloration  with  hydrochloric  acid. 

3-Methylindole,  or  scatole, 

NH 


C.CHS 

is  present  in  faeces,  and  occasions  the  unpleasant  odour.  It  is  also 
found  in  a  species  of  wood  grown  in  India,  and  is  formed  in  the 
putrefactive  decay  of  proteins,  or  by  fusing  proteins  with  caustic 
potash. 

Tryptophan  or  indolealanine,  CiiHi202N2,  is  an  important  decom- 
position-product of  proteins  (252,  5)  and  an  indole  derivative.  It 
is  synthesized  by  treating  indole  with  chloroform  and  potassium 
hydroxide  in  alcoholic  solution.  3-Indolealdehyde  (I.)  is  formed  as 
an  intermediate  product,  and  condenses  with  hippuric  acid  to  indolyl- 
benzoylaminoacrylic  acid  (II.).  On  treatment  with  sodium  and 
alcohol,  the  double  bond  of  this  compound  adds  two  hydrogen 
atoms  and  the  benzoyl-group  is  simultaneously  eliminated,  with 
formation  of  racemic  tryptophan  (III.)  : 


CH:OCOOH 

NH-COC6HS 

N 

II. 

CH2-CH-COOH 

NH2 
NH 

Tryptophan 

III. 


578  ORGANIC  CHEMISTRY.  [§  404 

Indigo. 

404.  The  constitution  of  indigo  is  inferred  from  its  formation 
from  isatin  chloride,  obtained  by  the  interaction  of  isatin  and 
phosphorus  pentachloride.  On  reduction  with  zine-dust  and  acetic 
acid,  it  is  transformed  into  indigo: 

C6H4<^N>CC1  +  C1 


Since  on  treatment  with  sulphuric  acid,  and  subsequent  reduc- 


,.  ,.   ..     ,.  ,       ,,.      ,  ,  =C  —  C=C-C6H4   . 

tion,  o-ainitroaiptienylaiacetyiene,   •  ,  is  con- 

NO2  NO2 

verted  into  indigo,  the  two  isatin-residues  in  the  latter  must  be 
united  by  a  carbon  linking. 

Indigo  has  long  been  known  as  one  of  the  most  beautiful 
blue  dyes,  and  is  very  permanent,  being  unaffected  by  light,  acids, 
alkalis,  or  washing.  It  can  be  prepared  .from  certain  plants, 
among  them  Indigofera  sumatrana  and  7.  arrecta.  Formerly 
these  plants  were  cultivated  on  a  large  scale  in  Bengal  in  India  — 
whence  the  dyestuff  derived  its  name  —  as  well  as  in  Java,  China, 
Japan,  and  South  America;  but  since  its  introduction, 
synthetic  indigo  (405)  has  to  a  very  great  extent  displaced  the 
natural  product,  even  in  the  countries  mentioned,  and  the  com- 
petition has  become  so  keen  as  to  lead  to  the  abandonment  of 
many  indigo-plantations,  and  the  financial  ruin  of  their  proprietors. 
Indigo  is  not  present  in  the  plant  as  such,  but  in  combination  as 
the  glucoside  indican,  which  occurs  chiefly  in  the  leaves,  and 
can  be  extracted  with  hot  water.  It  is  crystalline,  and  has  the 
formula  C^HijOeNjSH^O.  In  addition  to  the  glucoside,  the 
leaves  contain  an  enzyme,  the  activity  of  which,  like  that  of  all 
enzymes,  is  destroyed  by  boiling  water:  hence,  when  indican 
itself  is  to  be  prepared,  hot  water  must  be  employed  in  the  extrac- 
tion. With  cold  water,  both  indican  and  the  unchanged  enzyme 
dissolve,  and  the  glucoside  decomposes  into  dextrose  and 
indoxyl,  C8H7ON,  or  NH 

C6H4/  \CH, 

XCOH^ 


§  405]  INDIGO.  579 

a  substance  which  is  moderately  stable  in  acid  solution,  but  in  dilute 
alkaline  solution  is  quickly  oxidized  to  indigo  by  atmospheric 
oxygen. 

The  manufacture  of  indigo  from  the  plants  containing  it  is 
carried  out  by  the  method  indicated.  The  leaves  of  the  indigo- 
plant  are  allowed  to  remain  immersed  in  lukewarm  water  for  some 
hours:  the  aqueous  extract  is  "  churned  "  by  a  revolving  water- 
wheel  with  wooden  paddles,  which  aerates  it,  and  thus  oxidizes  the 
indoxyl  to  indigo.  The  oxidation-process  is  facilitated  by  the 
addition  of  slaked  lime  to  make  the  liquid  faintly  alkaline.  The 
indigo  formed  sinks  to  the  bottom,  is  removed  by  filtration,  and 
dried.  It  is  put  on  the  market  in  the  form  of  small  cubes. 

In  addition  to  the  blue  dye,  indigotin,  commercial  indigo  con- 
tains indiglucin,  indigo-brown,  and  indirubin;  these  substances 
can  be  extracted  by  water,  alcohol,  and  alkalis,  in  which  indigotin 
is  insoluble.  Indigotin  is  a  dark-blue  powder,  which,  when  rubbed, 
has  a  copper-like  lustre.  It  can  be  sublimed  in  vacuo,  so  that  it  is 
possible  to  determine  its  vapour-density.  It  is  insoluble  in  most 
solvents,  but  can  be  crystallized  from  nitrobenzene  or  aniline.  It 
dissolves  in  fuming  sulphuric  acid,  with  formation  of  sulphonic  acids. 

405.  On  account  of  the  great  industrial  importance  of  indigo, 
many  attempts  have  been  made  to  synthesize  it.  One  method  is 
commercially  successful,  enabling  the  artificial  product  to  be  sold 
at  a  much  lower  price  than  that  formerly  obtained  for  natural 
indigo.  It  yields  pure  indigotin,  which  is  also  an  advantage. 
This  method  is  employed  by  the  BADISCHE  ANILIN-  UND  SODA- 
FABRIK  of  Ludwigshafen-on-Rhine.  Anthranilic  acid,  or  o-amino- 

V-TT 

benzoi'c  acid   (346),   C6H4<  combines  with  monochloro- 


acetic  acid  to  form  phenylglycine-o-carboxylic  acid: 

NHH+aH2c.co2H 


C6H4<C[0_(OH 

Phenylglycine-o-carboxylic  acid 

Fusion  with  sodium  hydroxide  transforms  this  compound  into 


indoxyl,  CeH^  ^CH,  which  in  alkaline  solution  is  con- 

NC(OH)^ 
verted  by  atmospheric  oxidation  into  indigo. 


580  ORGANIC  CHEMISTRY.  [§405 

The  production  of  indigo  by  this  method  has  been  rendered 
possible  by  the  disovery  of  a  satisfactory  process  for  the  manu- 
facture of  anthranilic  acid.  It  is  obtained  by  oxidizing  naphtha- 
lene to  phthalic  acid  (347),  which  can  be  converted  into  anthranilic 
acid,  with  intermediate  formation  of  phthalimide  (346). 

On  reduction  in  alkaline  solution,  indigo  takes  up  two  hydrogen 
atoms,  with  formation  of  indigo-white,  Ci6H12O2N2,  a  white, 
crystalline  substance,  the  phenolic  character  of  which  is  proved 
by  its  solubility  in  alkalis.  In  alkaline  solution  it  is  speedily 
reconverted  into  indigo  by  atmospheric  oxidation,  a  reaction 
employed  in  dyeing  with  this  substance.  The  dye  is  first  reduced 
to  indigo-white,  and  the  fabric  thoroughly  soaked  in  an  alkaline 
solution  of  this  compound:  on  exposure  to  the  air,  the  indigo- 
blue  formed  is  fixed  on  the  fibres.  The  process  is  technically 
known  as  "  indigo  vat-dyeing." 

The  reduction  of  indigo  to  indigo-white  is  variously  carried  out 
in  the  dyeing-industry  according  to  whether  wool,  silk,  or  cotton 
is  to  be  dyed.  Reduction  is  best  effected  with  a  salt  of  hyposul- 
phurous  acid,  H2S2O4  ("  Inorganic  Chemistry,"  83),  for  the  two 
first  named.  The  solution  is  mixed  with  zinc  hyposulphite,  and 
treated  with  excess  of  milk  of  lime,  which  precipitates  zinc  hydrox- 
ide. The  indigo  is  mixed  with  water,  and  warmed  to  about  60° 
with  the  solution  of  calcium  hyposulphite,  a  concentrated  alkaline 
solution  of  indigo-white  being  obtained  in  a  short  time.  On  adding 
sufficient  water  to  it  in  the  dyeing-vat,  the  bath  is  ready  for  use. 
The  hyposulphite  reduction-process  possesses  the  advantage 
that  the  reduction  stops  at  the  formation  of  indigo-white,  so  that 
almost  none  of  the  indigo  is  lost. 

Indigo  is  the  longest-known  and  most  important  member  of  the 
series  of  vat-dyestuffs.  They  include  pigments  insoluble  in  water, 
but  characterized  by  their  ready  reduction  to  a  form  soluble 
in  dilute  alkali,  their  attraction  in  this  condition  by  vegetable  and 
animal  fibres,  and  their  subsequent  reoxidation  on  the  fibre  to  the 
original  insoluble  condition. 

The  vat-method  of  dyeing  has  great  advantages  over  other 
processes,  since  the  fabric  requires  no  previous  treatment  by  mor- 
danting or  otherwise,  and  both  the  preparation  of  the  vat  and  the 
operation  of  dyeing  are  usually  carried  out  at  the  ordinary  tem- 
perature. A  further  advantage  is  the  very  fast  nature  of  the 
colours  imparted  by  these  dyestuffs. 


§  405]  INDIGO.  581 

Vat-dyestuffs  derived  from  indigo,  and  others  related  to  anthra- 
quinone,  are  known.  Those  of  the  first  class  are  called  indigoids, 
and  contain  the  chromophore-group,  — CO*C*C«CO — . 

Substitution  by  halogen  of  the  hydrogen  atoms  in  the  benzene- 
nuclei  of  indigo  produces  a  marked  change  in  colour  only  when  the 
hydrogen  atoms  occupying  the  para-positions  to  the  carbonyl-groups 
are  replaced.  Symmetrical  dibromoindigo, 


CO 


NH 


is  the  celebrated  "Purple  of  the  ancients"  employed  in  antiquity 
for  dyeing  Tyrian  purple.  It  was  formerly  obtained  from  the 
colour-yielding  glands  of  the  mollusc  Murex  brandaris  in  the  form 
of  a  colourless  substance  converted  into  the  dye  by  the'  action 
of  light. 

Thioindigo  is  a  reddish-blue  derivative  in  which  two  sulphur 
atoms  replace  the  two  imino-groups.  The  tint  of  the  dyestuff  can 
be  so  much  altered  by  substitution  as  to  render  possible  the  pro- 
duction of  almost  every  colour. 


ALKALOIDS. 

406.  Plants  of  certain  families  contain  substances,  usually  of 
complex  composition  and  basic  character,  called  alkaloids.     Their 
classification  in  one  group  is  of  old  standing,  and  had  its  origin  in 
an  idea  similar  to  that  which  prevailed  concerning  the  vegetable 
acids  (i)  prior  to  the  determination  of  their  constitution.     Just  as 
the  latter  have  been  subdivided  into  different  classes,  such  as 
monobasic,  polybasic,  aliphatic,  and  aromatic  acids,  so  it  has  become 
apparent  that  the  individual  alkaloids  can  be  arranged  in  different 
classes.     Most  of  the  alkaloids  are  related  to  pyridine,  quinoline,  or 
isoquinoline,  while  a  smaller  number  belong  to  the  aliphatic  series. 
Some  of  the  latter  class  are  described  along  with  the  compounds  of 
similar  chemical  character:  among  them  are  be  tame  (242),   mus- 
carine  (229),  choline  (160),  caffeine,  and  theobromine  (272). Only 
alkaloids  which  are  derivatives  of  pyridine  are  described  in  this 
chapter:   to  them  the  name  alkaloids,  in  its  more  restricted  sense, 
is  applied,  the  other  substances  being  known  as  vegetable  bases. 

PROPERTIES. 

407.  It  is  seldom  that  an  alkaloid  is  present  in  more  than  one 
family  of  plants :  ^rnany  families  do  not  contain  them.     The  occur- 
rence of  alkaloids  is  almost  entirely  confined  to  dicotyledonous 
plants.     Only  a  few,  such  as  conilne  and  nicotine,  are  liquids:  most 
of  them  are  crystalline.     Many  are  optically  active  and  Isevo-rota- 
tory:    it  is  very  exceptional  for  them  to  exhibit  dextro-rotation. 
They  have  an  alkaline  reaction  and  a  bitter  taste:  most  of  them  are 
insoluble  in  water,  more  or  less  soluble  in  ether,  and  readily  soluble 
in  alcohol.     Most  are  insoluble  in  alkalis,  but  dissolve  in  acids, 
forming  salts  which  are  sometimes  well-defined,  crystalline  sub- 
stances. 

Many  alkaloids  can  be  identified  by  characteristic  colour-reac- 
tions. Some  substances  precipitate  many  of  the  alkaloids  from 
their  aqueous  or  acid  solution:  such  general  alkaloid-reagents  are 
tannin  (346),  phosphomolybdic  acid,  mercuric  potassium  iodide, 

582 


§  408]  ALKALOIDS.  583 

KI.HgI2  ("Inorganic  Chemistry,"  273),  and  others.    Some  alka- 
loids are  excessively  poisonous. 

Strong  tea  is  sometimes  employed  as  an  antidote,  the  tannin 
present  precipitating  the  alkaloid,  and  rendering  it  innocuous. 

Most  of  the  alkaloids  are  tertiary  amines,  and  consequently 
yield  addition-products  with  methyl  iodide :  none  of  them  possesses 
the  character  of  a  primary  amine.  Many  contain  acid-residues  or 
methoxyl-groups :  the  former  are  removed  by  saponification,  effected 
by  heating  with  bases  or  acids,  the  latter  by  heating  with  hydriodic 
acid,  which  yields  methyl  iodide.  Hydroxyl-groups  can  be  iden- 
tified in  the  ordinary  way  with  acid  chlorides  or  acetic  anhydride 
(89  and  90).  On  dry  distillation,  or  on  heating  with  zinc-dust, 
substituted  pyridines  are  sometimes  formed. 

On  account  of  the  complex  constitution  of  the  alkaloids,  the 
structures  of  many  of  them  remain  undetermined,  so  that  a  rational 
classification  is  not  yet  possible. 

408.  In  the  extraction  of  the  alkaloids  from  plants  the  latter 
are  cut  up  into  fine  pieces  and  lixiviated  with  acidified  water  in  a 
conical  vat  tapering  towards  the  bottom,  where  there  is  a  layer 
of  some  material  such  as  glass-wool  or  lint.     The  effect  is  that  the 
acidified  water  gradually  sinks  through  a  thick  layer  of  the  sub- 
stance under  extraction,  a  process  technically  known  as  "  percola- 
tion."    Dyes,   carbohydrates,  inorganic  salts,  etc.,  are  dissolved 
along   with   the   alkaloids.     When   the  alkaloid   is   volatile  with 
steam,  it  can  be  separated  by  this  means  from  the  liquid,  after 
making  the  mixture  alkaline:   when  it  is  comparatively  insoluble, 
it  can  be  obtained  by  filtration.     Further  purification  is  always 
necessary,  and  is  effected  by  crystallizing  the  free  alkaloid  or  one 
of  its  salts  several  times. 

INDIVIDUAL  ALKALOIDS. 

Coniine,  C8H17N. 

409.  The  synthesis  ofconime  is  described  in  390.    It  is  present 
in  spotted  hemlock  (Conium  maculatum) ,  and  is  a  colourless  liquid 
of  stupefying  odour.     It  boils  at  167°,  is  but  slightly  soluble  in 
water,  and  is  very  poisonous. 


584  ORGANIC  CHEMISTRY.  [§§410,411 

Nicotine,  Ci0H14N2. 

410.  Nicotine  is  present  in  combination  with  malic  acid  and 
citric  acid  in  the  leaves  of  the  tobacco-plant  (Nicotiana  tabacum). 
It  is  a  colourless,  oily  liquid,  which  is  laevo-rotatory,  and  readily 
soluble  in  water.     It  has  a  tobacco-like  odour,  which  is  not  so 
marked  in  a  freshly-distilled  sample  as  in  one  which  has  stood  for 
some  time.     It  boils  at  246-7°,  and  is  excessively  poisonous.     It 
quickly  turns  brown  on  exposure  to  air.     It  is  a  ditertiary  base: 
on  oxidation  with  potassium  permanganate,  it  is  converted  into 
nicotinic  acid  (391),  proving  it  to  be  a  /^-derivative  of  pyridine. 

The  constitutional  formula  of  nicotine  is 

CH2  —  CH/j 

I      I 

—  CH      CH2j 
N-CH3 

with  a  hydrogenated  pyrrole-nucleus  methylated  at  the  nitrogen 
atom,  and  a  ^-substituted  pyridine-nucleus.  The  formula  also  ex- 
presses the  facts  that  nicotine  is  a  ditertiary  basis  and  that  it  yields 
nicotinic  acid  on  oxidation.  This  formula  is  proved  by  the  syn- 
thesis of  nicotine;  which  yields  an  optically  inactive  modification 
resolvable  into  components.  The  laevo-rotatory  isomeride  is  iden- 
tical with  natural  nicotine.  The  dextro-rotatory  form  is  much  lesa 
poisonous  than  the  laevo-rotatory,  and  also  differs  from  it  in  other 
respects  in  its  physiological  action. 

Atropine,  Ci7H23O3N. 

411.  Atropine  is  present  in  the  berry  of  the  deadly  nightshade 
(Atropa  belladonna)  and  in  the  thorn-apple,  the  fruit  of  Datura 
stramonium.     It  is  crystalline,  melts  at  115-5°,  and  is  very  poison- 
ous.      It  exercises  a  "mydriatic  "  action  —  that  is,  when  dropped 
in  dilute  solution  on  the  eye,  it  expands  the  pupil:   for  this  reason 
it  is  employed  in  ophthalmic  surgery.     It  is  optically  inactive. 
On  heating  with  hydrochloric  acid  or  caustic  soda  at  120°,  it  takes 
up  water  and  yields  tropine  and  tropic  acid: 


Atropine  Tropine  Tropic  acid 


§  411]  ALKALOIDS.  585 

It  can  be  regenerated  from  these  two  substances  by  the  action 
of  hydrochloric  acid.  Atropine  'is,  therefore,  the  tropine  ester 
of  tropic  acid,  which  is  a-phenyl-/?-hydroxypropionic  acid, 

^       OTT 

The  constitutions   of  atropine  and  tropine 


are: 

I.          II. 
HoC  —  OH  -  CH.9  H2C  —  CH  -  CH 

I 


N-CH3  CHO.CO-CH.CH2OH 


N-CH3  CHOH. 

I 


and 
H2C— CH CH2  H2C— CH CH2 

Atropine  Tropine 

This  formula  for  tropine  was  proposed  by  WILLSTATTER  and  is 
based  on  the  decomposition-products  of  this  substance.  They 
are 

1.  Methylsuccinimide,  (I.)  indicating  the  presence  of  a  tetra- 
hydropyrrole-nucleus.* 

2.  Tropidine,  obtained  through  elimination  of  water  by  heat- 
ing with  potassium  hydroxide  or  dilute  sulphuric  acid: 

C8H15ON-H20   =  C8Hi3N. 

Tropine  Tropidine 

Tropidine  can  be  converted  into  a-ethylpyridine  (II.),  proving 
that  tropine  contains  a  pyridine-ring. 

Ecgonine  (412)  is  a  carboxylated  tropine:  it  breaks  down 
to  suberone  (III.),  indicating  the  presence  of  a  ring  of  seven 
carbon  atoms  in  the  tropine  molecule.  It  has  also  been  estab- 
lished by  the  usual  methods  that  tropine  is  a  tertiary  base,  and 
contains  a  hydroxyl-group : 

CH2—  C(X 

I.  |  >N-CH3  ;     II. 

>— C(X 


CH2 


CH2  —  CH2  —  CH2v 

III.  |  \CO. 

CH2  —  CH2  —  CH2^ 


*  Cf.  footnote,  395. 


586  ORGANIC  CHEMISTRY.  [§§  412, 413 

Cocaine,  C17H21O4N. 

412.  On  account  of  its  use  as  a  local  anaesthetic,  cocaine  is  the 
best  known  of  the  alkaloids  present  in  coca-leaves  (Erythroxylon 
coca).  It  is  crystalline,  is  readily  soluble  in  alcohol,  and  melts  at 
98°.  On  heating  with  strong  acids,  a  benzoyl-group  and  a  methyl- 
group  are  eliminated,  with  formation  of  ecgonine,  (I.),  so  that  the 
constitution  of  cocaine  is  represented  by  II. : 


CH2  •  CH CH  •  COOH        CH2 .  CH CH  •  COOCH3 

N.CH3  CHOH       ;  N-CH3  CHO.COC6H5. 

CH2  •  CH CH2  CH2  •  CH- 


By  benzoylating  and  methylating  ecgonine,  cocaine  is  regenerated. 
Ecgonine  is  a  tropinecarboxylic  acid. 

Morphine,  Ci7Hi9O3N. 

413.  Morphine  is  the  longest-known  alkaloid :  it  was  obtained 
from  opium  in  1806  by  SERTURNER.  Opium  is  the  dried  juice  of 
the  seed-capsules  of  Papaver  somniferum,  a  variety  of  poppy.  It 
is  a  very  complex  mixture,  containing  caoutchouc,  fats,  resins, 
gums,  sugars,  proteins,  mineral  salts,  meconinic  acid, 

(CH3O)2C6H2(CH2OH)(COOH), 

some  more  organic  acids,  and  other  substances,  together  with 
numerous  alkaloids.  Twenty  of  the  last-named  have  been  identi- 
fied :  of  these  morphine  is  present  in  largest  proportion,  and  con- 
stitutes about  10  per  cent,  of  opium. 

Morphine  is  crystalline,  and  melts  with  decomposition  at  230°. 
It  is  slightly  soluble  in  water,  is  without  odour,  and  is  employed 
as  an  anodyne  and  narcotic. 

The  reactions  of  morphine  indicate  that  one  of  its  three 
oxygen  atoms  is  linked  as  phenolic  hydroxyl,  proved  by  its 
solubility  in  alkalis;  the  second  is  present  as  alcoholic  hydroxyl; 
and  the  third  has  an  ether-linking.  On  distillation  with  zinc- 
dust  it  yields  phenanthrene,  C14H10,  so  that  the  empirical  formula, 
may  be  expanded  to 

C17H1903N  =  C3H1GN[C14][0][OH][HOH]. 


§  413]  ALKALOIDS.  587 

Treatment  with  methyl  iodide,  in  alkaline  solution  methylates 
the  phenolic  hydroxyl;  the  simultaneous  addition  of  methyl 
iodide  at  the  nitrogen  (I.)  proves  morphine  to  be  a  tertiary  base. 
The  product  formed  is  identical  with  the  methyl-iodide  derivative 
of  codeine.  On  treatment  of  this  substance  with  aqueous 
sodium  hydroxide,  hydriodic  acid  is  eliminated,  and  another 
tertiary  base  containing  a  like  number  of  carbon  atoms  formed. 
It  is  called  a-methylmorphimethine  (II.).  On  heating  with  acetic 
anhydride,  methylmorphimethine  yields  a  product  free  from 
nitrogen  (III.),  and  one  containing  nitrogen  (IV.)  The  first 
is  methylmorphol  or  4-hydroxy-3-methoxy-phenanthrene,  convert- 
ible by  further  methylation  into  a  synthetic  product,  dimethyl- 
morphol  (386),  a  reaction  indicating  its  structure.  The  second 
is  hydroxyethyldimethylamine,  CH2OH-  CH2  -  N(CH3)2 : 

CH30 .  C6H2— CH2  CH30 .  C6H2— CH 

0< 


HO.C6H  —  CH 
I 
CH2  —  CH2.N(CH3)2 


c 

C6H4-CH 
III. 

HO-CH2—  CH2-N(CH3)2 
IV. 

By  combining  these  facts  with  others  it  has  been  possible  to 
assign  provisionally  to  morphine  the  structural  formula 

H 


HO/\H 
A/\H2 

O       I        |H 


It  represents  morphine  as  a  combination  of  a  partially  hydro- 
genated  dihydroxyphenanthrene  containing  an  ether-linked  oxygen 


588 


ORGANIC    CHEMISTRY. 


[§414 


atom  with  a  hydrogenated  pyridine-nucleus  having  the  nitrogen 
atom  linked  to  methyl. 

Heroin  is  the  diacetyl-derivative  of  morphine. 


Narcotine, 

414.  Narcotine  is  present  in  opium  to  the  extent  of  about  6  per 
cent.,  its  percentage  being  next  to  that  of  morphine.  It  is  crystal- 
line, melts  at  176°,  and  is  slightly  poisonous.  It  is  a  weak  tertiary 
base,  its  salts  readily  undergoing  hydrolytic  dissociation.  It  con- 
tains three  methoxyl-groups,  and  has  formula  I.  Nornarcotine 
has  the  formula  C19Hi4O4N(OH)3.  On  hydrolysis,  narcotine 
yields  cotarnine  (II.),  a  derivative  of  tsoquinoline,  and  the  anhy- 
dride of  meconinic  acid,  or  meconin  (III.) : 

OCH3 
C      CH 


OC-C 


N-CH3     O-OC-C 
CH2          CH3O-C 


CH 


CH   CH2 


I. 

Narcotine 


OCH3 

C      CHOH 
OC-C/\/\ 


GH2<^ 

OC- 


ii 

Urli 


\/ 

CH    CH2 
II. 

Cotarnine 


\/ 

C 
OCH3 


O CH2 

I         'C 

oc-c 


\s 

C 


CH 


OCH3 
III. 

Meconin 


Bromine  converts  narcotine  into  dibromopyridine. 


415] 


ALKALOIDS. 


589 


Quinine,  CooH^C^N^. 

415.  The  barks  of  certain  trees  of  the  Cinchona  and  Remya 
families  contain  a  great  number  of  alkaloids:  of  these  twenty-four 
have  been  isolated,  but  it  is  probable  that  more  are  present.  The 
most  important  of  them,  on  account  of  its  anti-febrile  effect,  is 
quinine.  Cinchonine,  CigH^O^,  is  the  next  best-known:  its 
physiological  action  is  similar  to  that  of  quinine,  but  is  less  pro- 
nounced. 

In  addition  to  alkaloids,  these  barks  contain  various  acids,  such 
as  quinic  acid,  quinovic  acid,  and  quinotannic  acid:  neutral  sub- 
stances, such  as  quinovin,  quina-red,  etc.,  are  also  present. 

Quinine  is  very  slightly  soluble  in  water,  and  is  laevo-rotatcry. 
In  the  anhydrous  state  it  melts  at  177°,  and  at  57°  when  it  conr 
tains  three  molecules  of  water  of  crystallization.  It  is  a  strong 
base,  and  both  N-atoms  are  tertiary.  It  unites  with  two  equiva- 
lents of  an  acid.  In  dilute  solution  the  salts  of  quinine  exhibit  a 
splendid  blue  fluorescence,  which  serves  as  a  test  for  the  base. 

The  constitution  of  quinine  has  been  elucidated,  chiefly  through 
the  researches  of  SKRAUP  and  of  KONIGS,  the  latter  assigning  to 
it  the  formula 


II. 


CH.OH 


CH 


CH.CH:CH2 


CH2 


which  expresses  the  following  properties  of  quinine.     On  fusion 
with   potassium   hydroxide   quinine   yields   quinoline,   p-methyl- 


590  ORGANIC  CHEMISTRY.  (§416 

quinoline  or  lepidine,  and  p-methoxyquinoline  from  the  part  of 
the  molecule  numbered  I.  in  the  structural  formula;  and  /?- 
ethylpyridine  from  part  II.  On  oxidation,  a/^-pyridinetri- 
carboxylic  acid  is  obtained,  also  from  part  I.  In  addition, 
quinine  is  a  ditertiary  base,  and  contains  a  hydroxyl-group  and  a 
methoxyl-group.  Its  additive  power  indicates  the  presence  of  a 
double  carbon  bond. 

The  formula  of  cinchonine  differs  from  that  of  quinine  in  having 
methoxyl  replaced  by  hydrogen. 

Strychnine,  C21H2202N2. 

416.  Three  extremely  poisonous  alkaloids,  strychnine,  brucine  f 
and  curarine,  are  present  in  the  seeds  of  Strychnos  nux  vomica,  as 
well  as  in  others  of  the  Strychnos  family.  Little  is  known  of  the 
chemical  nature  of  curarine,  although  it  has  been  much  studied 
from  a  physiological  standpoint :  when  administered  in  small  doses, 
it  produces  total  paralysis.  Strychnine  and  brucine  cause  death, 
preceded  by  tetanic  spasms — that  is,  contraction  of  the  muscles; 
curarine  is,  therefore,  employed  as  an  antidote. 

Strychnine  is  crystalline,  and  melts  at  265° ;  it  is  almost  insoluble 
in  water.  It  is  a  monohydric,  tertiary  base,  only  one  of  its  .N- 
atoms  .exhibiting  basic  properties.  On  fusion  with  potassiun 
hydroxide,  it  yields  quinoline  and  indole;  and  when  distilled  with 
slaked  lime,  it  is  converted  into  /?-picoline  (389).  Heating  with 
zinc-dust  .produces  carbazole  (382)  and  other  substances. 

W.  H.  PERKIN,  JUN.,  and  ROBINSON  consider  the  chemical 
properties  of  strychnine  to  be  represented  most  completely  by 

the  formula 

CH2     CH 


CH2 

Brucine  differs  from  strychnine  in  having  methoxyl-groups 
as  substituents  in  positions  1  and  4. 


INDEX. 


The  basis  of  the  arrangement  of  this  index  is  three-fold: 

(1)  The  numbers  refer  to  pages. 

(2)  In  all  instances  of  possible  ambiguity  as  to  the  identity  of  the  principal  references, 
they  are  given  in  old-style  figures. 

(3)  Where    a  reference  is  a  sub-division  of  a  principal  heading,  it  is  indented  "one 
em  space  for  each  word  of  the  principal  heading  not  repeated.      Portions  ofjwords  followed 
by  a  hyphen  are  treated  as  words  for  the  purposes  of  this  arrangement. 


A. 


Abbreviated  thermometers,  32. 
ABEL,  SIR  FREDERICK,  38. 
Absolute  alcohol,  56. 
Acetal,  254,  255. 

Chloro-,  298. 

Acetaldehyde,  67,  132,  133,  137-140, 
143-145,  166,  175,  177,  179,  182, 
189,  195,  227,  228,  232,  254,  255, 
269,  300,  316,  416,  485,  524,  558. 
-ammonia,  137,  557. 
Synthesis  of,  189. 
Acetals,  137-138,  185,  280. 
Acetamide,  128. 

hydrochloride,  128. 
Acetaminohydrazobenzene,  p-,  409. 
Acetates,  112. 

Acetic  acid,  2,  15,  54,  59,  93,  105,  106, 
108,    110-112,    117-123,    125, 
132,  145,  172,  188,  189,  192, 
203,  220,  221,  225,  252,  300, 
302,  391,  407,  420,  421,  429, 
444,  484,  566,  578. 
Glacial,  16,  30,  in,  402,  541. 
Chloro-,  202,  203,  220,  221,  226, 

316,  318,  319,  579. 
Synthesis  of,  189. 

anhydride,  120,  136,  138,  191,  192, 
260,  277,  295,  431,  444,  472,  485, 
568,  583,  587. 
fermentation,  286. 
Acetoacetic  acid,  301. 

ester.     See  ethyl  acetoacetate. 

synthesis,  301-304. 
Acetoanilide,  402,  405,  459. 
Acetobromodextrose,  277. 
Acetoferric  acetate,  112. 
Acetone,  16,  54,  59,  60,  85,  99,   132, 
135,  145,  146,  153,  154,  160-162, 
165,  166,  177,  179,  181,  182,  186, 
189,  253,  297,  300,  302,  310,  311, 
387,  513,  531'. 
Synthesis  of,  189. 


Acetonitrile,  103. 
Acetonuria,  146. 
Acetonylacetone,  254,  304,  567. 
Acetophenone,  429,  443,  472. 
Acetoxime,  135,  310. 

hydrochloride,  135. 
Acetyl-acetone,  253,  254,  307. 

chloride,  119,  120,  121,  136,  249, 
253,  300,  306,  349,  424,1429,  561. 

-coumaric  acid,  484. 

-group,  109. 

-mesidine,  491. 

-phenetidine,  461. 

-salicylic  acid,  471. 
Acetylene,    158-162,    176,    183,    184, 
189,  341,  387,  443,  566. 

bromide,  166. 

-dicarboxylic  acid,  216. 
Acid-albumins.     See  meta-proteins. 

anhydrides,  120,  208,  209. 

azides,  129,  358,  359. 

chlorides,  119,  120,  128,  133. 

decomposition,  301,  302,  303. 

hydrazides,  129. 

-urei'des.     See  ureides. 
Acids,  CnH2nO2,  105-118,  130,   169, 
191,  192. 

CnH2n-2O2,  169-173. 

CnH2_4O2,  173-174. 

C4H6O2,  171. 

A cidylgly collie  acid  esters,  323. 
Aci-modifications,  439. 
Aconitic  acid,  218. 

Acraldehyde.  167,  175,  176,  189,  190, 
262,  263,  557,  570,  572. 

-acetal,  176. 

-ammonia,  175,  557. 

-aniline,  572. 

Acrolein.     See  acraldehyde. 
Acrose,  263. 

Acrylic  acid,  167,  169,  170,  175,  317. 
Addition-reactions,  229. 
Adipic  acid,  199,  504,  543. 

anhydride,  377. 

591 


592 


INDEX. 


Adjacent  compounds,  385. 
Adrenaline,  485. 
Agaricus  muscarius,  298. 
Air-condenser,  21. 
Alanine,  316,  319,  334,  336. 

d-,  322. 

1-,  322. 

nitrile,  316. 

Albumin,  328,  333,  338. 
Albuminates.     See  meta-protelns. 
Albuminoids.     See  sdero-proteins. 
Albumins,  326,  328,   329,  330,   331, 

332. 

Albumose,  329. 
Alcohol.     See  ethyl  alcohol. 
Alcoholates.     See  alkoxides. 
Alcoholic  fermentation,  54,  268,  269, 

285-288,  320. 
Alcohols,  Aromatic,  441. 

CnH2n+i-OH,  49-66,   77,   78,  80, 
83,  86,  119-121,  128,  129,  147. 
Higher,  66. 
Aldehyde.     See  acetaldehyde. 

-resin,  139,  140. 

sulphite  compounds,  134. 
Aldehydes,   130-145,   148,   159,   183, 

185-187,  198,  224,  259,  310,  374, 

426-428. 
Aldehydo-acids,  299. 

-alcohols.     See  sugars. 
Aldohexoses,  257,  259,  273. 
Aldol,  139,  140,  176,  267. 
Aldopentoses,  273,  274. 
Aldoses,  257,  258. 
Aldoximes,  135,  136. 
Alicyclic  compounds,  157,  373,  375- 

379- 

Aliphatic  compounds,  34,  35-371. 
Alizarin,  544,  548-550. 

diacetate,  549. 

Alkali-albumins.     See  meta-prote'ins. 
Alkaloid-reagents,  582. 
Alkaloids,  288,  474,  582-590. 
Alkoxides,  49,  66,  67,  74,  78,  106,  147. 
Alkyl-anilines,  406. 

-groups,  37. 

halides,  69-72,  74,  78,  83,  84,  96, 
97,  147,  153,  165,  179. 

-hydrazines,  88. 

magnesium  halides,  100,  101,  105, 
122,  135,  314. 

nitrites,  91. 

-nitrolic  acids,  93. 

-sulphinic  acids,  80. 

-sulphonic  acids,  80. 

sulphonyl  chlorides,  80. 

-sulphuric  acids,  72,  73,  79,  149. 

-ureas,  355. 
A.lkylenes.     See  olefines. 


Allantoine,  363,  364. 

^4ZZocinnamic  acid,  445. 

Allotropy  of  carbon,  19. 

Alloxan,  362-364,  366. 

Alloxantine,  363. 

Alryl  alcohol,  165,  166,  167,  168,  175, 

184,  188,  189,  190,  195. 
-aniline,  572. 
bromide,  166,  183,  184. 
chloride,  165,  166. 
iodide,  166,  168,  169,  171,  189,  190. 
isothiocyanate,  348. 
magnesium  bromide,  171. 
sulphide,  168. 
Allylene,  157,  158. 
Aluminium  acetate,  112,  465. 
acetylacetone,  254. 
mellitate,  481. 
Amber,  205. 
Amic  acids,  202. 
Amidines,  129. 
Amidoximes,  129. 
Amine  hydrohalides,  84. 
Amines,  82-91,  95,  136,  395,  401-412, 

479. 

Amino-acetal,  298. 
-acetaldehyde,  298. 
-acetic  acid.     See  glycine. 
-acids,  316-323,  334. 
Di-,  334. 

Dibasic  mono-,  334,  336. 
Hydroxy-,  334. 
Monobasic  mono-,  334. 
-alcohols,  197. 
-aldehydes,  298. 
-anthraquinone,  2-,  551. 
-azo-dyes,  466. 

-benzene,  419,  420,  462-464,  466, 

467. 

-barbituric  acid,  364. 
-benzenesulphonic    acid,    p-.     See 

sulphanilic  acid. 
-benzole  acid,  o-.     See  anthranilic 

acid. 

acids,  475,  476,  495. 
-benzoylformic  acid,  o-,  576. 
-butyric  acid,  7-,  317. 

Lactam  of  7-,  317. 
-caproi'c  acid,  at-.     See  lysin  e. 
-chlorides,  128,  129. 
-cinnamaldehyde,  o-,  573. 
-cinnamic  acid,  o-,  575. 
-glutaric  acid,  a-,  320,  331,  334,  336. 
-guanidine,  361. 
-5-guanino-n- valeric  acid,  a-.     See 

arginine. 

-iso-butylacetic  acid.     See  leucine. 
-ketones,  298. 
-mandelic  acid,  o-,  576. 


INDEX. 


593 


Amino-/3-methylvaleric  acid,  a-.     See 

tsoleucine. 

-naphthalene,  89,  490. 
-naphthol,  i  :  2-,  541. 
-nonoic  acid,  9-.  174. 
-phenol,  a-,  461. 

p-,  411,  453,  457,  460,  461. 
-phenols,  461. 

-phenyl-acetic  acid,  o-,  576. 
-arsinic  acid,  p~,  461,  462. 
-p-acetamiriophenylamine,  p-} 

409. 
-propionic  acid,  a-.     See  alanine. 

0-,  317. 

-succinamic  acid.     See  asparaginc. 
-succinic  acid.     See  aspartic  acid. 
-thiophen,  568. 

hydrochloride,  568. 
-valeric  acid,  a~,  334. 
Ammonium  carbamate;  358. 
cyanide,  342. 
formate,  341,  342. 
zso-cyanate,  354,  355. 
oxalate,  202,  340. 
picrate,  452. 
succinate,  209. 
thiocyanate,  360,  361. 
Amygdalin,  342,  427. 
Amyl  acetate,  iso-,  121. 

alcohol,  Normal,  51,  52,  78,  147, 

309,  505,  452. 

alcohols,  51,  54,  62,  63,  64,  390. 
bromide,  Normal  primary,  71 
chloride,  Normal  primary,  71. 
iodide,  Normal  primary,  71. 

Optically  active,  63/64. 
isovalerate,  iso-,  121. 
nitrite,  252.  518. 
-sulphuric  acids,  151. 
Amylene,  Normal,  148. 
Amylenes,  147,  14S,  151,  153. 
Amylocellulose,  291. 
Amyloid,  295,  296.  ' 
Anaesthetics,  180. 
Analysis,  Example  of,  10,  11. 
Angelic  acid,  169. 
Anhydro-bases,  461. 

-formaldehydeaniline,  403. 
Anilides,  402. 

Aniline,  259,  266,  296,  396,  403,  404, 
405,  408-412,  414,  419-422,  428, 
434,  457,  459,  460,  463,  495.  529, 
530,  543,  572,  579. 
-black,  463,  464. 
-blue,  530. 

-dyes.     See  coal-tar  colours. 
hydroarsenate,  461. 
hydrochloride,  404-406,  419,  420, 
'530. 


Aniline  hydrogen  sulphate,  462. 

nitrate.  413. 

-yellow,  466. 

Animal  fats,  34,  113-115. 
Anisanilide,  433. 
Anisole,  400,  401. 
ANSHUTZ,  545. 
Anthracene,  534,  544,  546,  548,  549. 

-oil,  389,  534,  544,  551. 
Anthranilic  acid.  475,  476,  492,  579, 

580. 

Anthranol,  548. 
Anthraquinol,  547,  548. 

Disodium  derivative  of,  547. 
Anthraquinone,   545,  548,   549,  550, 
581. 

oxime,  547. 

-sulphonic  acids,  549. 
Anthrone,  548. 

Antifebrine.     See  acetoanilide. 
Antimony  pentamethide,  97. 
Antipyrine,  570. 
Antiseptics,  182,  400,  471. 
Apiose,  277. 
Apricot-stones,  265. 
Arabinosazone,  265. 
Arabinose,   262,   264,   265/275-277, 
387,  288,  298. 

-methylphenylhydrazone,  273. 
Arabitol,  193,  262,  265. 
Arabonic  acid,  265. 
Arginine,  334,  336,  361. 
AJgol;2387~~ 
ARMSTRONG,  397. 
Aromatic  compounds,  34,  373,  380- 

553- 

"  Arsacetin,"  462. 
Arsenobenzene,  434. 
Arsines,  95,  96. 
Arsinobenzene,  434. 
Artificial  camphor,  517. 
Asparagine,  245,  287,  320. 
Aspartic  acid,  320,  331,  336. 
Asperula  odorata,  484. 
Asphalt,  39. 

"Aspirin."     See  acetylsalicylic  acid. 
Asymmetric  carbon  atoms,   64,   65, 
321,  322. 

nitrogen  atoms,  98,  99. 

silicon  atoms,  97. 

sulphonium  compounds,  98,  99. 

sulphur  atoms,  98. 

synthesis,  288,  289. 

tin  atoms,  100. 
Atomic  refraction,  157. 
Atoms,  Law  of  the  even 

45  . 

"At  oxyl,"  462. 
Atropa  belladonna,  584. 


594 


INDEX. 


Atropine,  584,  585. 
Autogenous  welding,  161. 
Auxochromei'c  groups,  464,  465. 
Azelai'c  acid,  173,  199. 
Azo-benzene,  408,  409,  411,  412,  434, 
464. 

-dyes,  460,  464-468. 
Azoxy-benzene,  408,  411,  412. 

-phenetole,  p-,  408. 
Azulminic  acid,  341. 

B. 

Bacillus  acidi  lavolactici,  247. 
BADISCHE  ANILIN-UNDSODA-FABRIK. 

579. 
BAEYER,   VON,    148,    156,   209,   216, 

263,  314,  381,  428,  455,  508,  527, 

564,  572,  575. 
Balsam  of  Peru,  423. 

Tolu,  380,  423. 
BAMBERGER,  412. 
Barbituric  acid,  364. 
Barium  acetate,  172. 

carbide,  342. 

cyanide,  342. 

ethoxide,  67. 

ethylsulphate.  73. 

stearate,  172.' 

thiocyanate,  346. 

trithiocarbonate,  352. 
BAUMANN-SCHOTTEN  reaction,  425. 
BAUMHAUER,  VON,  57. 
BECKMANN,  136. 

-transformation,  136,  174,  346,  433. 
Beer,  56,  110. 
Beeswax,  122. 
Behenolic  acid,  222. 
BEILSTEIN'S  test,  5. 
Benzal  chloride,  426,  438,  444,  525. 
Benzaldehyde,    277,    342,   411,    422, 
424,  426-428,  440,  441,  443,  444, 
507,  526,  533,  562. 

-ammonia,  427. 

-phenylhydrazone,  428. 
Benzaldoximes,  431. 
Benzamide,  423,  425,  426. 
Benzaniside,  433. 
Benzanta'alc'oxime  (a),  431,  433. 
Benzene,  16,  30,  34,  101,  160,  333, 
351,  373',  378,  380-391,  393,  395, 
430,  436,  446-452,  457,  462,  476, 
477.  495,  496,  504,  505,  507,  524, 
525,  535,  545,  546,  552,  557,  566- 
568. 

Constitution  of,  380-384. 

-diazohydroxide,  419. 

-diazonium  chloride,  416-421,  465, 
466,  566,  568. 


Benzene-diazonium    hydroxide,    410, 

414,  415,  419. 
nitrate,  413,  414. 
sulphate,  416. 
-sulphonic  acid,  460. 
xanthate,  417. 

-disulphonic  acid,  m-,  450,  452. 
o-,  450. 
p-,  450. 

Molecular  weight  of,  11. 
-sulphonamide,  398. 
-sulphonic  acid,  386,  397,  417,  505, 

518,  568. 

-sulphonyl  chloride,  397,  398. 
-s?/ndiazo-chloride,  418. 
-hydroxide,  415,  418. 
Benzhydrol,  429. 
Benzidine,  409,  523,  524,  539,  540. 

-diazonium  chloride,  540. 
Benzidine  sulphate,  409. 

-transformation,  409,  525. 
Benzil,  533. 

dioximes,  533. 
Benzilic  acid,  533. 
Benzine,  38. 

Benzole  acid,  29,  318,  33,  380,  421- 
424,    425,    426,   428,    429,    437, 

440,  441,    444,    468,    469,    498, 
505,  5075  523,  530,  538,  564. 

anhydride,  425. 

iminoether,  425. 

sulphinide,  o-.     See  saccharin. 
Benzoin,  533,  562. 
Benzo-nitrile,  422,  426,  431,  441,  555. 

-o-sulphamide,  469,  470. 

-phenone,  429,  430,  524. 
-oximes,  431. 

-purpurins,  539,  540. 

-quinone,  454,  457-459,  460,  464, 

494,507,526,540,541. 
dioxime,  458. 
mono-oxime,  453,  458. 

-trichloride,  422,  438. 
Benzoyl-benzoic  acid,  o-,  546. 

chloride,  423-425,  429,  438,  485. 

-formic  acid,  289. 

-hydrogen  peroxide,  428. 

-piperidine,  555. 

-serine,  335. 
Benzpinacone,  429. 
Benzsynaldoxime  (/3  or  iso),  431,  433. 
Benzyl  alcohol,  422,  426,  427,  441. 

-amine,  438,  441,  442,  543. 

bromide,  436,  437. 

chloride,  430,  436,  437,  438,  440, 

441,  524,  532. 
cyanide,  440. 
halides,  436-438. 
iodide,  398,  437-438. 


INDEX. 


595 


Benzylidene-aniline,  428. 

-phenylhydroxylamine,  411. 
BERNTHSEN,  527* 
BERTHELOT,  2,  28,  122. 
BERZELIUS,  1. 
Betai'ne,  318,  319,  582. 
Betai'nes,  319. 
BEYERINCK,  286. 
Bimolecular  reactions,  85,  125,  126, 

256. 

Bioses.     See  dioses. 
BIOT,  63. 

Bismarck-brown,  466,  467. 
Bismuthines,  97. 
Bismuth  mercaptides,  79. 
Bismuthonium  bases,  97. 
Bitter  almonds,  342,  396,  427. 
Biuret,  327,  356,  357. 

-reaction,  327,  329,  330,  333,  338, 

356. 

Blasting  gelatine,  193. 
BOESEKEN,  429. 
Boiling-point  apparatus,  EYKMAN'S, 

17,  18. 

Determination  of,  31. 
BONDT,  184. 

Borneo  camphor.     See  borneol. 
Borneol,  518,  520. 
Bornyl  fumarate,  289. 

pyroracemate,  /-,  289. 
Brain-substance,  197. 
Bran,  265. 

Branched  chains,  45. 
Brandy,  56. 

Brassidic  acid,  173,  221,  223. 
Brassy  lie  acid,  199. 
BRAUN,  VON,  555. 
BREDIG,  323. 
BREDT,  520. 

Brisant  effect,  193,  296,  349. 
Bromination-method  of  VICTOR 

MEYER,  183. 
Bromlauge,  104,  357. 
Bromo-acetaldehyde,  262. 

-acetic  acid,  220. 

-acetylidene,  166. 

-anthraquinone,  546. 

-benzene,  11,  381,  386,    389,    394, 
395,  404,  405,  416,  417,  422, 
435,  449,  495,  538. 
-sulphonic  acids,  449. 

-benzole  acid,  m-,  468. 
p-,  468,  492,  493. 

-benzophenone,  431. 

-benzoylbenzoi'c  acid,  546. 

-butylene,  mono-,  154. 

-camphorsulphonic  acid,  99. 

-erucic  acid,  222. 

-ethylamine,  479. 


Bromo-fumaric  acid,  214,  215. 
-isobutyric  acid,  171. 
-malei'c  acid,  214. 
anhydride,  215. 
-malonic  acid,  232. 
-naphthalene,  a-,  538. 
-phenol,  o-,  450,  498. 

p-,  450,  498. 

-phthalic  anhydride,  546. 
-propionic  acid,  a-,  229,  322. 
-propylene,  0-,  166. 
-succinic  acid,  210. 
-thiophen,  567. 
-toluenes,  437. 
Bromoform,  181. 
Brucine,  590. 
BRUHL,  157. 
BRUYN,  LOBRY  DE,  67. 
BUCHNER,  EDUARD,  285,  286. 
BUNSEN,  97,  357. 
Butane,  36,  37,  41,  42,  46. 

cyclo-,  375,  376. 
Butanol,  cyclo-,  376. 
Butanone,  cyclo-,  376. 
BUTLEROW,  154. 
Butter,  113. 

of  antimony,  380. 
Butyl-acetylene,  158. 
alcohol,  iso-,  51,  52,  60. 
Normal,  51,  52,  60. 
Secondary,  51,  52,  60,  125. 
-amine,  n-,  87. 

cyclo-,  376. 
bromide,  cyclo,  376. 

Normal  primary,  71. 
bromopropionate,  iso-,  230. 
-carbinol,  -iso-,  51,  62,  320. 
Secondary,  51,  62,  320. 
Tertiary,  51. 

-carbpxylic  acid,  cyclo-,  376. 
chloride,  Normal  primary,  71. 
derivatives,  cyclo-,  375,  376. 
-dicarboxylic  acid,  cyclo-,  375. 
-group,  37. 
iodide,  iso-,  153. 

Normal  primary,  71. 

secondary,  193. 
Tertiary,  149,  153. 
-sulphuric  acid,  Tertiary,  149. 
Butylene,  cyclo-,  376. 
iso-,  149,  153,  154. 
Normal,  148. 
pseudo-,  220. 

Butyraldehyde,  Normal,  131. 
Butyric    acid,    iso-,    113,   220,   224, 

515. 
Normal,  107,  108,  113,  118,  139, 

170,  171,  260,  269,  333. 
fermentation,  269. 


596 


INDEX. 


Butyrolactone,  226,  231. 
Butyryl  chloride,  Normal,  31. 
-group,  109. 

C. 

Cacodyl,  97. 

chloride,  97. 

oxide,  97. 

-test  for  acetates,  97,  112. 
Cadaverine.     See  pentamethylenedia- 

mine. 

Caffeine,  365,  366,  367-369,  582. 
Calcium  acetate,  54,  no,  132,  146, 
189. 

acetylene.     See  calcium  carbide. 

adipate,  376,  377,  503. 

benzoate,  380. 

carbamate,  358. 

carbide,  161,  162,  348. 

citrate,  248. 

cyanamide,  348. 

diphenate,  524. 

ethylsulphate,  72. 

gly  collate,  226. 

-isobutyrate,  114. 

-n-butyrate,  114. 

oxalate,  206. 

pimelate,  503. 

salicylate,  Basic,  471. 

suberate,  378. 

succinate,  206. 

tartrate,  238. 
Calculation  of  formulae,  9-18. 

percentage-composition,  9-11. 
Calico-printing,  112,  249. 
Camphane,  516,  517,  520. 

-group,  518. 
Camphor,  518-521. 

-odour,  518. 

-quinone,  519. 

Synthesis  of,  520. 

-sulphonic  acid,  d-,  99. 
Camphoric  acids,  519-521. 

anhydride,  519. 
Camphoronic  acid,  519-520. 
Camphors,  378,  392,  503,  518-521. 
Cane-sugar.     See  sucrose. 
Caoutchouc,  162,  184,  352,  521,  522, 

586. 

Capric  acid,  108,  145,  172,  303,  507. 
Caproiic  acid,  108,  113. 
Caprylic  acid,  108. 
Caprylonitrile,  104. 
Caramel,  279. 
Carane,  516,  517. 
Carbamic  acid,  358. 

carbamyl  chloride,  423. 
Carbamide.     See  urea. 


Carbazole,  544,  590. 
Carbides,  metallic.     See  metallic  acet- 
ylenes. 

Carbinol.     See  methyl  alcohol. 
Carbinols,  52. 
Carbocyclic    compounds,    373,    375- 

563. 

Carbohydrates.     See  sugars. 
Carbolic  acid.     See  phenol. 

oil,  389,  398,  534. 
Carbon  chains,  45,  46. 

disulphide,  28,  181,  309,  352,  353, 

544,  567. 

oxy-chloride.     See    carbonyl    chlo- 
ride. 

-sulphide,  347,  348,  353. 
suboxide,  205. 
tetra-bromide,  36,  179. 
-chloride,  36,  179,  181. 
-fluoride,  393. 
Carbonic  acid,  351. 

esters,  352. 
Carbonyl  chloride,  180,  312,  351,  354, 

407,  422,  423,  429. 
-haemoglobin,  332. 
Carbostyril,  575. 
Carbylamines.     See  isonitriles. 
Carbylamine-test,  104,  403. 
CARIUS,  8. 
Carone,  517. 
Carvacrol,  514,  520. 
Carvone,  514,  515. 
Carvoxime,  515. 
Casein,  328,  335,  336. 
Casei'nogen,  328. 
Castor-seed,  114. 
Catalytic  action  of  aluminium  halides, 

430,  437. 

antimony  pentachloride,  184. 
calcium  chloride,  144. 
copper,  133. 
ferric  halides,  183,  393,  437,  446, 

468,  498. 

hydrogen  ions,  323. 
mineral  acids,  125,  138,  144,  145. 
nickel,  35,  134,  151,  505. 
palladium,  505. 

rhodium    and    other    platinum- 
group  metals,  110. 
sulphuric  acid,  144,  145. 
Catechol,  453,  454,  458,  473,  485,  550. 
Catechu-tannin,  474. 
CAYLEY,  47. 
Cellose,  295. 
Celluloid,  296. 
Cellulose,  294-297. 
Cetyl  alcohol,  66. 
CHATTAWAY,  350. 
Chelidonic  acid,  311,  312. 


INDEX. 


597 


Chelidoniwn  majus,  311. 
Chemical  reduction-products,  410. 
Chemistry  of  silicon,  97. 
Cherry-gum,  265. 
CHEVREUL,  115. 
Chitin,  298. 
Chitonic  acid,  298. 
Chitose,  298. 

Chloral,  58,  179,  221,  254-256. 
alcoholate,  25c. 

hydrate,  254.  255,  256,  299,  305. 
Chloro-acetic  acids,  221. 
-acetone.  153,  158,  164. 
-acetyl  chloride,  485. 

-catechol,  485. 
-aniline,  m-,  493. 

p-,  418,  463. 
-benzene,  386,  394,  416,  418,  447, 

449,  498,  538. 

-sulphonic  acid,  p-,  449,  460. 
s?/ndiazocyanide,  p-,  419. 
-benzoic  acid,  m-,  468. 
o-,  468. 
p-,  422,  468. 

-benzonitrile,  p-}  418,  419. 
-benzophenone,  431. 
-butyric  acid,  «-,  220. 
ft-,  220. 
7-,  220. 

-butyronitrile,  7-,  321. 
-caffeine,  368. 
-carbon,  447. 
-carbonic  esters,  352. 
-ether,  195. 
-ethers,  195. 
-formic  esters.     See  chlorocarbonic 

esters. 

-c?/dohexane,  506. 
-methylene,  180. 
-naphthalene,  a-,  538. 
-nitro-aniline,  493. 

-benzene,  m-,  447,  498. 
o-,  447. 

p-,  447,  493,  498. 
-phenol,  o-,  450,  498. 

p-,  450,  498. 
-propionic  acid,  a-,  319. 
-propylene,  «-,  164,  165. 

/3-,  164,  165. 
-pyridine,  -0,  555,  566. 
-succinic  acid,  233. 
d-,  321. 
1-,  321. 
-toluene,  o-,  436,  499. 

p-,  436. 

Chloroform,  16,  28,  58,  104,  179-181, 
221,  255,  256,  342,  482,  483,  525, 
566,  577. 
Chlorophyll,  564. 


j  Chlorophyll-grains,  289. 
Chloropicrin,  360. 
Choline,  196,  197,  582. 
Chondrin,  328,  330,  331. 
Chondroitinsulphuric  acid,  331. 
Chondrosin.  331. 
Chromogens,  464. 
Chromophore-groups,  464,  581. 
Chromoprotems,    329,  332. 
Chrysoiidine,  466. 
Chrysin,  472. 
Cinchomeronic  acid,  575. 
Cinchonine,  589,  590. 

malate,  233. 

mandelates,  441. 

d-tartrate,  246. 

Z-tartrate,  246. 
Cineol,  511,  512. 
Cinnamaldehyde,  444. 
Cinnamic  acid,  444,  445. 
Allo-,  445. 

acids,  iso-,  445. 
Cinnamyl  alcohol,  443,  444. 
Citral.     See  geranial. 
Citric  acid,  248,  249,  282,  584. 
Citromyces  glaber,  248. 

pfefferianus,  248. 
CLAISEN,  252,  253,  301. 
Classification  of  organic  compounds, 

34. 

Clupeme,  336. 
Coagulated  proteins,  329. 
Coagulation,  326,  327. 
Coal,  158. 

-gas,  35,  147,  158,  161,  388,  391 
534. 

-mine-explosions,  36. 

-tar.     See  tar. 

colours,  388,  404. 
Cocaine,  586. 
Cocoa,  366. 
Codeine,  587. 

methyl-iodide  derivative,  587. 
Coefficient  of  distribution,  29. 
Coffee,  366. 

-tannin,  474. 
Cognac,  56. 
Coke,  388. 
Collagens,  330,  331. 
Collidine,  557,  558. 
Collidines,  557,  558. 
COLLIE,  313. 
Collodion,  296. 
Colloids,  326,  338. 
Colophonium,  480. 
Colour-bases,  528,  529. 
Combustion-furnace,  5. 

of  peat,  141. 
wood,  141. 


598 


INDEX. 


Combustions,  5-7. 
Compound  ethers.     See  esters. 
Condensation,  140. 
Condensed  rings,  373,  534. 
Confectionery,  268. 
Conglomerate,  247. 
Congo-dyes,  539,  540. 

-red,  539,  540. 
Confine,  558,  559,  582,  583. 

iso-,  548. 

Conium  maculatum,  583. 
Conjugated  proteins,  329,  331,  332. 

linking,  383. 

system,  163. 
Constancy  of  substitution-type,  Rule 

of,  497. 

Constitutional  formula,  44,  51. 
Constitution  of  alcohols, 

CnH2n+^OH,  49-51. 

Contact-difference  of  potential,  371, 

410,  411. 
Copper  acetylacetone,  254. 

acetylene,  159,  161. 

disodium  tartrate,  239.  , 

mercaptides,  79. 

-oxide  test,  4. 

-zinc  couple,  150. 
Coral,  331. 
Corneiiin,  331. 
Cotarnine,  588. 
Cotton,  294. 

-wool,  295,  296. 
Coumaric  acid,  483,  484. 
Coumarin,  484. 
Coumarinic  acid,  483,  484. 
CRAFTS,  389,  390,  429. 
Cream  of  tartar,  238. 
Creosote-oil,  389,  398,  534. 
Cresol,  m-,  509. 

o-,  470,  515. 

p-,  333,  400. 
Cresols,  398,  400. 
CRISMER,  91. 
Critical  temperature  of  solution,  90, 

91. 

Croconic  acid,  377. 
Crotonaldehyde,  140,  176. 

-ammonia,  557. 
Crotonic  acid,  169,  170,  171,  173,  174, 

176,  210,  212,  220,  225. 
iso-,  171. 

Solid.     See  crotonic  acid. 
Cryoscopic  methods,  14-17,  338. 

solvents,  14,  15,  16,  391. 
Crystalloids,  326. 
Crystal-violet,  528. 
Cumene,  391. 
Cupric  cyanide,  340. 

phenylpropiolate,  443. 


Cupric  xanthate,  353. 
Cuprous  cyanide,  340. 

xanthate,  353. 
Curarine,  590. 
Current-density,  207. 
CURTIUS,  263,  323. 
Cyamelide,  344,  345,  350,  354. 
Cyanamide,  334,  348,  356,  360,  361. 
Cyanic  acid,  344,  345,  346,  347. 

iso-,  345,  354,  355. 
esters,  345. 

iso-,  345,  346,  353,  355,  358. 
Cyanides,  340,  341,  342-344. 
Cyano-acetic  acid,  202,  203. 
-benzoi'c  acid,  o-,  480. 
-hydrin-synthesis,    134,    135,    224, 
227,  248,  261-264,  265,  270,  275, 
276,  288,  303. 
-propane,  a-,  184. 
-quinolines,  574. 
Cyanogen,  200,  340,  341. 
chloride,  345. 
derivatives,  340-350. 
Cyanuric  acid,  344,  345,  349,  350, 

354,  357. 

Insoluble.     See  cyamelide. 
iso-,  349,  350. 
bromide,  349. 
chloride,  345,  350. 
esters,  349,  350. 

iso-,  345,  349,  350. 
Cyclic    compounds,    34,     157,    254, 

373-590. 
hydrocarbons,      CnHon,     375-379, 

503-505. 
Cymene,  380,  391,  392,  508,  509,  516, 

521. 

m-,  517. 

p-.     See  cymene. 
Cysteine,  335. 
Cystine,  335,  336. 

D. 

Datura  stramonium,  584. 

DAVY,  J.,  351. 

Decamethylenedicarboxylic  acid,  199. 

Decane,  41. 

Definition  of  organic  chemistry,  1. 

Dehydromucic  acid,  563. 

DEIMAN,  184. 

Denaturation  of  albumins,  326. 

ethyl  alcohol,  54,  58. 
Deoxy-caffeme,  369. 
-compounds,  369. 
Depressimeter,  EYKMAN'S,  16,  17. 
Depression  of  the  freezing-point,  14- 

17. 
Molecular,  15,  16. 


INDEX. 


599 


Desmotropy.     See  taulomerism. 
Detection  of  carbon,  3,  4. 
carbonyl-group,  136. 
halogens,  4,  5. 
hydrogen,  3,  4. 
nitrogen,  4. 
oxygen,  5. 
phosphorus,  4. 
sulphur,  4.  5. 
water  in  acetone  and  alcohols, 

57,  91. 

Determination  of  boiling-point,  31. 
melting-point,  31. 
molecular  weight,  11-18. 
of  specific  gravity,  32. 
vapour-density,  12,  13. 
Developers,  201,  455,  461. 
Dextrin,  291,  293,  294. 
Dextrins,  291. 

Dextrose,  54,  227,  248,  266-269,  270, 
272,  275,  277-279,  281,  284, 
286-291,  295,  342,  470,  474,  548, 
578. 

a,  267,  268,  281. 
j8-,  267,  268,  281. 
e-,  267,  268. 

Diabetes  mellitus,  146,  266. 
Diacetoneamine,  145. 
Diacetyl,  252,  300,  301. 
Diacetylenedicarboxylic  acid,  217. 
Dialdehydes,  250,  251. 
Dialkyl-phosphines,  95. 
-phosphinic  acids,  96. 
Diallyl,  251. 
Diamines,  196,  209. 
Diamino-azobenzene.  See  chrysoldine. 
-dihydroxyarsenobenzene,  462. 
dihydro  chloride.     See  salvarsan. 
-stilbene,  p-,  532. 
-trihydroxydodecanic  acid,  335. 
Diamylene,  151. 
Dianthracene,  544. 
Diastase,  55,  277,  291. 
Diazo-acetic  ester.     See  ethyl  diazo- 

acetate. 

-aminobenzene,  419,  420. 
-compounds,  323,  324,  413-420. 
anti-,  413,  418. 
syn-,  413,  417,  418. 
-hydrates,    anti-.     See    diazohy- 

droxides,  anti-. 
Diazonium    compounds,    398,    403, 

413-420,421. 
Dibasic     acids,     198-217,     232-245, 

476-481. 

Dibenzalci/cZohexannone,  507. 
Dibenzhydroxamic  acid,  438. 
Dibenzyl,  532,  533. 
-amine,  441. 


Dibromo-acetic  acid,  299. 
-benzene,  m-,  381,  446,  492. 

o-,  381,  483. 

p-,  381. 

-brassidic  acid,  222,  223. 
-butyric  acid,  174. 
-erucic  acid,  221,  222. 
-indigo,  Symmetrical,  581. 
-menthane,  514. 
-menthone,  509. 
-nitroethane,  93. 
-propane,    aat'-.     See    trimethylene 

bromide. 

-propane,  aj8-,  184. 
-pyridine,  588. 
-succinic  acid,  213,  214,  233. 

iso-,  213,  214,  215. 
-thiophen,  567. 
Dicarbonyl-bond,  279. 
Dichloro-acetyl,  255. 
-acetic  acid,  220,  221. 
-acetone,  248. 
-benzene,  m-,  446,  498. 

o-,  498. 

p-,  463,  498. 
-ethylene,  184. 
-hydrin,  Symmetrical.  See  glycerol 

dichlorohydrin. 

Didiphenylene-ethylene,  525. 
Diethoxy-8-chloropurine,  2  :  6-,  368. 
Diethyl.     See  also  ethyl. 
-acetonedicarboxylate,  455. 
-acetylenedicarboxylate,  568,  569. 
-carbinol,  51. 
carbonate,  351,  354,  358. 
c?/cZobutyldicarboxylate,  375. 
diacetylsuccinate,  304. 
dibromomalonate,  305. 
dihydrocollidinedicarboxylate,  557. 
disodiomalonate,  203,  218,  375. 
disulphide,  79. 
ether.     See  ether. 
malate,  233. 

malonate,  203-205,  455,  456. 
monosodiumalonate,      203,      204, 

206,   217,   218,  306,    321,    455, 

480. 

oxalate,  202,  312. 
phloroglucinoldicarboxylate,  456. 
succinate,  207,  504. 
succinylsuccinate,  504. 
sulphate,  72,  73. 
-jsulphonedimethylmethane.        See 

sulphonal. 

xanthochelidonate,  312. 
Dihydric  alcohols.     See  glycols. 

phenols,  453-455. 
Dihydro-cinnamic   acid   o-carboxylie 

acid,  542. 


600 


INDEX. 


Dihydro-naphthalene.     See  naphtha- 
lene dihydride. 

-pyrrole,  2  :  3-,  566. 
Dihydroxy-acetone.     See  glycerose. 

-acids,  233-245,  472,  473. 

-anthraquinone.     See  alizarin. 

-azobenzenesulphonic    acid.       See 


-benzene,  m-.     See  resorcinol. 
o-.     See  citechol. 
p-.     See  quinol. 
-flavone,  1  :  3-.     See  chrysin. 
-fluoran.     See  fluoresceln. 
-naphthalene,  2  :  6-,  541. 
-phenanthrene,  587. 
-xanthone,  1  :  2'-.     Seeenxanthone. 
Di-iodopurine,  367. 
Dii'sopropyl,  45. 
Diketo-cyclohexane,  p-,  504,  506. 

-piperazine.    See  glycine  anhydride. 
Diketones,  250-254. 
Dimethoxyphenanthrene.     See  di- 
f    methylmorphol. 
Dimethyl-acetylene,  160. 
-allene,  162. 
-alloxan,  366. 

-amine,  84,  87,  142,  406,  407. 
-aminoazobenzene,  420,  465. 

-sulphonic  acid.     See  helianthine. 
-aniline,   405-407,   420,   427,   465, 

526,  530. 

hydrochloride,  467. 
0-0-,  501. 
-arsinic  acid,  96. 
-benzenes.     See  xylenes. 
-cycZooctadiene,  1  :  5-,  521. 
-diethylmercaptole,  146. 
-ethylcarbinol,  51,  162. 
-ethylene,  Symmetrical,  148. 

Unsymmetrical,  148. 
-hexane,  2:5-,  48. 
-ketone,  132. 
-morphol,  553,  587. 
oxalate,  202. 
-phenylpyrazolone.       See    antipy- 

rine. 

-phosphinic  acid,  96. 
-pyridines.     See  lutidines. 
-pyrone,  312-314. 

hydrochloride,  313. 
sulphate,  73,  87,  92. 
-thiophen.     See  thioxen. 
Dinaphthol,  a-,  539. 

0-,  539. 

Dinitriles,  198. 

Dinitro-benzene,  m-,  446,  448,  494. 
o-,  448,  449. 
p-,  448. 
-cellulose,  296,  297. 


Dinitro-compounds,    195,     196,   448, 
449. 

-diphenyldiacetylene,  o-,  578. 

-ethane,  439,  440. 
aci-,  439. 

-a-naphthol,  540. 

-sulphonic  acid,  540. 

-phenol,  2  :  6-,  448. 

-stilbene,  p-,  533. 

-toluene,  1  :  2  :  4-,  501. 

o-o- ,  501. 

Dioses,  257,  264,  276-289. 
Dioxindole,  576,  577. 
Diozonides,  251. 
Dipentene,  513,  514. 

tetrabromide,  514. 
Dipeptides,  337,  338. 
Diphenic  acid,  524,  525,  551. 
Diphenyl,   389,  409,  435,   523,  524, 

551,  552. 
Diphenyl-amine,  402,  404,  405,  409, 


-ethane,     Symmetrical.       See    di- 

benzyl. 
Unsymmetrical,  524. 

-ethylene,  Symmetrical.     See  stil- 
bene. 

-methane,  430,  524. 
Diphenyleneketone,  524,  525. 
Dippe!' s  oil,  554,  564. 
Dipropyl,  44,  45. 
Direct  dyes,  465. 
Dispersion,  34. 
Distearin,  192. 
Distillation,  21-28. 

-apparatus,  21-24,  26,  27. 

-flask,  21. 

of  wood,  53. 
Divi-divi,  473. 
Dodeca-hydronaphthalene,  541. 

-methylenedicarboxylic  acid,  199. 
Dodecaiie,  37,  41. 
Dodecyl-group,  37. 
DORP,  VAN,  346,  475,  480,  575. 
Double  bonds,  154-157. 
DREWSEN,  572. 
Dry-cleaning  process,  38. 
Dulcitol,  193,  194,  273. 
DUMAS,  2,  7. 
Dutch  liquid,  184. 
Duty  on  alcohol,  58. 
Dyers'  broom,  472. 
Dynamite,  193. 


Earth-wax,  39. 
Ebonite.     See  vulcanite. 
Ebullioscopic  methods,  14,  16-18. 
solvents,  16. 


INDEX. 


601 


Ecgonine,  586. 
EDER'S  solution,  202. 
Egg-albumin,  328." 

-yolk,  197. 
EHRLICH,  320,  462. 
Eicosane,  41. 
Elai'dic  acid,  173,  174. 
transformation,  173. 
Elastin,  328,  330,  331,  336. 
Electric      conductivity,      molecular, 

34. 

Electrolytic  dissociation,  116-118. 
methods,  368-371,  409-412. 
reduction-products,  410. 
Electro-synthesis  of  acids,  207. 
Elements  in  carbon  compounds,  3. 
Elevation   of   the   boiling-point,    14, 

16-18. 

Emulsin,  290,  342,  440. 
Enantiomorphism,  246,  247. 
Enantiotropy,  430,  431. 
ENGLER,  39. 
Enolic  form,  308-310. 
Ensilage,  227. 
Enzymes,  54,  192,  247,  269,  277,  285- 

287. 

Eosin,  202,  478. 
Epichlorohydrin,  195. 
Equilibrium,  122-125. 
Ergot,  486. 
Errors  in  carbon-estimations,  9. 

hydrogen-estimations,  9. 
Erucic  acid,  169,  173,  221,  222. 
Erythritol,  193. 
Erythrose,  276. 
Erylhroxylon  coca,  586. 
Esterification,  121,  122-125. 
Ester-method,  FISCHER'S,  334,  335. 
Esters,  68-73,  91,  120-127,  128. 
Estimation  of  carbon,  5-7,  9-11. 

halogens,  8,  9. 

hydrogen,  5-7,  9-11. 
ions,  323. 

nitrogen,  7,  8,  10,  11. 

oxygen,  9-11. 

phosphorus,  8. 

sulphur,  8. 
Ethane,  36,  37,  41-43,  95,  100,  151, 

160,  183,  207. 
-tricarboxylic  acid,  206. 
Ethenylaniinophenol,  461. 
Ether,  16,  28-30,  73,  74~?6,  1 '    ,153, 

180,  195,  309,  314. 
Chloro-,  195. 

-synthesis,  WILLIAMSON'     7 
Ethers,  69,  74-76,  77,  78-8  )  1 

401. 

Chloro-,  193. 
Ethyl.     See  also  diethyl 


Ethyl  acetate,  107,  120,  121,  122-125, 
128,  253,  297,  301,  455. 

acetoacetate,    301-309,    557,    558r 
570. 

-acetylene,  158. 

d-alanine,  322. 

alcohol,  16,  30,  49-51,  52,  54-58, 
67,  69,  72,74-76,  78,  91,  110, 
120-126,  128,  137,  143,  150, 
179-182.  187,  188,  195,  204, 
250,  254,  255,  266,  268,  269, 
277,  299,  301,  304,  307,  309, 
320,  349,  416,  425,  509. 
Test  for.  See  iodoform-test. 

-amine,  87,  102,  103,  197,  407,  425. 

-benzene,  389,  391. 

benzoate,  423,  425. 

bromide,  69-71,  73,  389. 

n-butylacetoacetate,  303. 

butyrate,  121,  207. 

carbonate,  455. 

-carbylamine,  102,  103. 

chloride,  71,  180,  183. 

chloro-carbonate,    217,    306,    351, 

358,  423. 
-formate.     See    ethyl    chlorocar- 

bonate. 
-oxalate,  426. 

collidinedicarboxylate,  557. 

copper-acetoacetate,  312. 

cyanide,  102,  103. 

7-cyanopropylmalonate,  321. 

cyanurate,  345. 

diazoacetate,  323,  324,   378,   568, 
569. 

di-iodoacetate,  323. 

ether.     See  ether. 

formate,  531. 

fumarate,  218,  324,  570. 

glycollate,  225,  323. ' 

-gly collie  acid,  224,  225. 

-group,  37. 

hydrogen   sulphate.     See   ethylsul- 
phuric  acid. 

iodide,  49,  64,  71,  72,  74,  80,  85, 
91,  96,  107,  401. 

-/3-iodopropionate,  510. 

isocyanate,  345. 

magnesium  bromide,  101. 

maleate,  215. 

-mercaptan,  146. 

mesoxalate,  305. 

methanetricarboxylate,  217. 

methyl-n-butylacetoacetate,  303. 

monochloroacetate,  206,  218,  304, 
323. 

nitrate,  72. 

nitrite j  91. 

-nitrolic  acid,  93. 


602 


INDEX. 


Ethyl  n-octylacetoacetate,  303. 
orthoformate,  180. 
phosphate,  Normal,  72. 
potassium  malonate,  207. 

succinate,  207. 
psewdophenylacetate,  378. 
-pyridine,  a-,  585. 

0-,  590. 

-salicylic  acid,  472. 
sodio-acetoacetate,    301-304,    305- 

309. 

-cyanoacetate,  510. 
sulphate,  72,  73. 
sulphide,  79. 
-sulphonic  acid,  80. 
-sulphuric  acid,  72,  73,  75,  150,  151, 

397. 
Ethylene,  88,  148,  149,  150,  151,  152, 

153,  183,  184,  186. 
-bromohydrin,  479. 
bromide,  150,  151,  152,   158,   164, 

167,  184,  206,  375,  479. 
chloride,  152,  183,  184,  187,  188. 
cyanide,  206. 
-diamine,  196. 

oxide,  187,  188,  197,  209,  561. 
Ethylidene  chloride,  133,  152,  158. 
Eugenol,  483. 

iso-,  482. 
Euxanthone,  472. 
Exaltation   of   refraction,    521,    543, 

544. 

Extraction  with  solvents,  28-30. 
EYKMAN,  15-17. 


F. 

Faeces,  577. 
FARADAY,  391. 
Fats,  2,  39,  114,  115,  116,  172,  184, 

191,  192,  325,  586. 
Fatty  acids,  105-107,  108,  109-118. 
compounds.     See     aliphatic    com- 
pounds. 
FEHLING'S  solution,   239,   240,   258, 

331,  421. 

Fermentation,  54,  55,  285-288. 
butyric    acid.     See    butyric    acid, 

Normal. 

Ferric  acetate,  264. 
Aceto-,  112. 
Basic,  112. 
succinate,  206. 
thiocyanate,  347. 
Fibrin,  328. 
Fibrinogen,  328. 
Fibroin,  331,  336,  338. 
Filtering-flask,  30. 
Filtration,  30. 


Fire-damp,  35,  36. 

FISCHER,  EMIL,  234,  272,  277,  280, 

286,  288,  298,  322,  334-338,   365, 

367,  368,  474,  479. 
FITTIG,  226,  389,  394. 
FITTIG'S  synthesis,  389,  394,  538,  567. 
Flash-point,  38. 

apparatus  of  ABEL,  38. 
Flavone,  472. 

dyes,  472. 
Flax,  295. 
Fluoran,  478. 
Fluorene,  524,  525. 
Fluorescei'n,  478,  479. 
Fluoro-benzene,  497. 

-nitrobenzene,  o-,  497, 

p-,  497,  498. 
Force,  Vital,  1. 
Formaldehyde,  54,  88,  132,  141-143. 

263,  289,  403. 
Formaldoxime,  143. 
"  Formalin."     See  formaldehyde. 
Formamide,  128. 
Formates,  109. 
Formic  acid,  102,  108-110,  112,  118, 

141,  142,  145,  176,  180,  190,  191, 

200,  255,  269,  344,  349,  391,  563. 
Formonitrile.     See  hydrocyanic  acid. 
Formose,  263. 

Formulae,  Calculation  of,  9-11. 
Formyl  chloride,  427. 

-group,  109. 
Fortified  wines,  56. 
Fractional  crystallization,  30. 

distillation,  22-26. 

curves,  25. 
Fractionating-apparatus,  21. 

-columns,  23,  24,  55. 
FRANCHIMONT,  355,  405. 
FRIEDEL,  189,  389,  390,  429. 

and   Craft's   synthesis,    389,    390, 

429,  538. 

Fructosazone,  d-.     See  d-glucosazone. 
Fructose,  d-.     See  laevulose. 
Fruit-essences,  121. 

-sugar.     See  Icevulose. 
"Fulminating  mercury,"  349. 
Fulminic  acid,  349. 
Fumaric  acid,  210-215,  218,  233,  243, 

244,  484. 

Furan,  374,  561,  562,  566. 
Furfural.     See  furfur  aldehyde. 
Furfuraldehyde,  266,  562,  563. 
Furfuramide,  562. 
Furf  uran .     See  fur  an . 
Furfuro'in,  562. 

Furfurole.     See  furfuraldehyde. 
Furfuryl  alcohol,  562. 
Furs,  455. 


INDEX. 


603 


FURTH,  VON,  328.  1 

Fusel-oil,  55,  58,  60,  62,  151,  320. 


G. 


Galactonic  acid,  d-,  273. 

Galactose,  d-,  194,  265,  273,  278,  287, 

290. 

Gallic  acid,  455,  473,  474. 
Gall-nuts,  473,  474. 

-stones,  351. 
Gas,  Coal-,  35,  147,   158,   161,  388, 

391,  534. 

Gas-manufacture,  388. 
Gastric  juice,  333. 
GATTERMANN,  416,  482. 
Gauliheria  procumbens,  470. 
Gelatin,  143,  328,  330,  331,  336,  474. 
Gelatose,  329. 
Geranial,  176,  177. 
Geranic  acid,  176. 
Geraniol,  176,  509,  510. 
GERHARDT,  2. 
Germanium  alkides,  97. 
German  process  for  vinegar,  110. 
GERNEZ,  63. 
Gin,  56. 

Glacial  acetic  acid,  30,  1 1 1 . 
GLADSTONE,  150. 
Gliadin,  328. 
Gliadins,  328. 
Globin,  332. 

Globulins,  328,  329,  330. 
Globulose,  329. 

Gluconic  acid,  d-,  267,  272,  278,  279. 
Gluco-proteins,  328,  329,  332. 
Glucosamic  acid,  d-,  298. 
Glucosamine,  298. 

hydrochloride,  298. 
Glucosazone,  d-,  267,  270,  271,  273. 
Glucose,  d-.     See  dextrose. 

i-,  266. 

1-,  266,  287. 

Glucosides,  277,  279-281,  342,  470, 
548,  578. 

Artificial,  279-281. 
Glucosone,  d-,  271. 
Glue,  318. 
Glutamic    acid.      See    aminoglutaric 

acid,  a-. 

Glutamine,  320. 
Glutaric  acid,  199,  208,  265,  377. 

anhydride,  208. 
Glutelins,  328. 

Glyceraldehyde,  262,  263,  272. 
Glyceric  acid,  188,  300. 
Glycerol,  54,  114,  115,  175,  188-193, 
194,  195,  262,  268,  572. 


Glycerol-dichlorohydrin,  195,  248. 
Glycerophosphoric  acid,  197. 
Glycerosazone,  262. 
Glycerose,  262. 
Glyceryl  diacetate,  192. 

monoformate.     See  monoformin. 

trinitrate.     See  nitroglycerine. 
Glycine,  224,  316,  317,  318,  319,  331, 
334,  336-338. 

anhydride,  337. 

Copper  salt  of,  318. 

ethyl  ester,  323,  337. 

hydrochloride  ethyl  ester,  318. 
Glycocoll.     See  glycine. 
Glycogen,  294. 
Glycol,  166,  186,  187,  188. 

-chlorohydrin,  149,  187. 

diacetate,  192. 

diethyl  ether,  187. 

monoethvl  ether,  187. 
Glycollaldehyde,  262,  334. 
Glycollic  acid,   224,   225,   226,   232, 

250,  270,  299. 
Glycollide,  226,  232. 
Glycolose.     See  glycollaldehyde. 
Glycols,  185-188,  198,  209. 
Glycyl-alanine,  338. 

-glycine,  336,  337. 
Glyoxal,  233,  250,  251,  299. 
Glyoxylic  acid,  299,  305,  324,  363. 

GOLDSCHMIDT,  420. 
GOMBERG,  531. 

Gout,  365. 

Granulose,  291. 

Grapes,  266. 

Grape-sugar.     See  dextrose. 

Graphic  method,  EYKMAN'S,  15. 

Green  oil.     See  anthracene-oil. 

GRIESS,  413. 

GRIGNARD,  100,  101,  105,  122,  135, 

314. 

Guaiacol,  453,  454,  483. 
Guanidine,  360,  361. 

thiocyanate,  360,  361. 
Guanine,  332,  365. 
Guanylic  acid,  329. 
Gum-arabic,  265. 

-benzoin,  380,  423. 

Cherry-,  265. 
Guncotton,  193,  296,  297,  349. 


H. 

HABER,  412. 
Hematin,  332. 

hydrochloride,  332. 
Haamin,  332. 

Hemoglobin,  329,  332,  336,  339. 
Haemoglobins.     See  chromo-proteins. 


604 


INDEX. 


Halochromy,  527. 
Halogen-benzenes,  393,  394,  437. 

-benzole  acids,  437,  468. 

-carriers,  393,  437,  446. 

derivatives  of  methane,  179-182. 
homologues,  182-185. 

-hydrins,  195. 

-phenols,  450. 

-substituted  acids,  219-223. 

-sulphonic  acids,  449. 

-toluenes,  436,  437. 
HAMBLY,  354. 
HANTZSCH,  413,  415,  418,  439,  528, 

557. 

Hard  water,  116. 
HARRIES,  251,  521. 
HATA,  462. 

Heating  substances,  20,  21. 
Heavy  oil.     See  creosote  oil. 
Helianthine,  460,  467. 
Heliotropin.     See  piperonal. 
HEMPEL,    Fractionating   column    of, 

23. 

Heneicosane,  41. 
Hentriacontane,  37,  41. 
Heptachloropropane,  181. 
Heptane,  41,  64. 

cyclo-,  505. 
Heptonic  acids,  264. 
Heptoses,  257,  264. 
Heptyl  alcohol,  Normal,  52. 
Hep ty lie  acid,  108,  303. 
Heroin,  588. 
Herring-brine,  87. 
Heterocyclic  compounds,  373,   554- 

590 

Hevea  brasiliensis,  521. 
Hexa-bromobenzene,  393. 
-chloro-benzene,  393. 

-ethane,  181,  183,  184. 
-contane,  36,  41. 
-decane,  41. 

-hydric  alcohols,  258,  260,  261,  271. 
-hydro-^enzoic  acid,  505,  507. 
-cymene.     See  menlhane. 
-phenol.     See  hexanol,  cyclo-. 
-hydroxy benzene,  377,  457. 
-methylbenzene,  160. 
-methylene.     See  hexane,  cyclo-. 

-tetramine,  142. 
-methyltriaminotriphenylmethane. 

See  crystal-violet. 
-phenylethane,  532. 
Hexane,  36,  41,  44,  45,  47,  85,  309. 
cyclo,  378,  381,  456,  503-506. 
derivatives,  cyclo-,  378,  381,  503- 

507. 

Hexanol,  cyclo-,  506,  507. 
Hexanone,  cyclo-,  503,  504,  507. 


Hexodioses,  257. 

Hexonic  acids,  258,  270-272. 

Hexoses,  257,  259-261,  264,  265,  266- 

276,  277,  286,  290,  304,  507,  563. 
Hexotrioses,  257,  289. 
Hexyl  alcohol,  Normal,  52. 

iodide,  Normal  secondary,  260. 

-methylamine,  cyclo-,  379. 
Hexylene,  148. 

Higher  alcohols,  CnH2n+1'OH,  66. 
Hippuric  acid,  318,  423. 
Histidine,  335,  336. 
Histories,  328. 
HOFF,  VAN  'T,  16,  64-66. 
HOFMANN,  83,  87. 
Homologous  series,  40. 
Honey,  269. 

Artificial,  563. 

-stone,  481. 

HOOGEWERFF,  346.  475,  480,  575. 
Hops,  56. 
Hordenine,  486. 
Hormathic  compounds.    See  aliphatic 

compounds. 
HOWARD,  349. 
Humic  substances,  273. 
Hydrazines,  420,  421. 
Hydrazinoacetic  acid,  324. 
Hvdrazo-benzene,  408,  409,  411,  412, 
523. 

-benzole  acid,  m-,  524. 
Hydrazones,  136,  137,  258,  259. 
Hydro-aromatic  compounds,  378,  387, 
503,  522. 

-benzamide,  427,  444,  562. 

-benzoin,  533. 

-carbons,  CnH2n,  76,  147-157/164, 

375-379,  503-507. 
CnH2n+2,  35-48,  148,  379. 

CnH2n-2,  157-163,  165. 

-cinnamide,  444. 

-cyanic  acid,  224,  228,  259,  277, 
286,  298,  319,  333,  341,  342,  344, 
347,  427,  482. 

-cyclic    compounds.      See    hydro- 
aromatic  compounds. 
-ferrocyanic  acid,  314. 
-naphthalenedicarboxylic  acid,  535. 
-phthalic  acids,  507. 
-quinone.     See  quinol. 
Hydrolysis,  104. 
Hydrolytic  dissociation,  115. 
Hydroxamic  acids,  94. 
Hydroxy-acetic    acid.     See    glycollic- 

acid. 
-acids,  Dibasic,  232-248. 

Monobasic,  223-232. 
-aldehydes,  481-483. 
-anthraquinones,  547-550. 


INDEX. 


605 


Hydroxy-azo-benzene,  o-,  408. 

p-,  408,  420,  465. 
-dyes,  466. 

-benzaldehyde,  p-,  482. 
-benzoic  acid,  m-,  472. 
o-.     See  salicylic  acid, 
p-,  472,  492. 
-butyric  acid,  a-,  139. 
/3-,  169,  225. 
•>-,  226,  231. 
-cinnamic  acid,  o-,  483. 
-cymene,  p-.     See  thymol. 
-ethyl-amine,  479. 

-dimethylamine,  587. 
-isobutyric  acid,  a-,  224. 
methyl-benzoic  acid,  o-,  477. 

-furfuraldehyde,  563. 
-3-methoxyphenanthrene,   4-.    See 

melhylmorphol. 
-phenyl-arsinic  acid,  p-,  462. 
-ethylamine,  p-,  486. 
propionic  acid,  p-,  483. 
-proline,  335. 
-propionic  acid,  a-.    See  lactic  acid. 

P-,  225,  226. 
-propylene,  /3-,  166. 
-quinoline,  2-.     See  carbostyriL 
-quinolines,  574,  575. 
-stearic  acid,  173. 
-succinic  acid.     See  malic  acid. 
-tetrahydr  opyrrolecarboxylic  acid . 

See  hydroxy proline. 
-toluenes.     See  cresols. 
Hyoscyamine,  dl.     See  atropine. 
Hypnone,  429. 
Hypoxanthine,  332,  365. 


I. 


Imino-chlorides,  129. 

-ethers,  129. 
Immiscible    liquids,    Separation    of. 

28-30. 

Increment  for  the  double  bond,  157. 
Indanthren-blue,  551. 

dyes,  551. 

"Indian  yellow."     See  euxanthone. 
India-rubber.     See  caoutchouc. 
Indican,  578. 

Indigo,  403,  428,  451,  475,  476,  575, 
578-581. 

-brown,  579. 

-sulphonic  acids,  428,  579. 

-vat-dyeing,  580. 

-white,  580. 
Indigofera  arrecta,  578. 

sumatrana,  578. 
Indiglucin,  579. 


Indigoids,  581. 
Indigotin,  579. 
Indirubin,  579. 
Indole,  575-577,  590. 

-alanine.     See  tryptophan. 

-aldehyde,  3-,  577. 

Indolylbenzoylaminoacrylic  acid,  577. 
Indophenin-reaction,  566. 
Indoxyl,  578,  579. 
Industrial  spirit,  58. 
Infusorial  earth.     See  kieselguhr. 
Ink,  473. 
Inoculation,  245. 
Inositol,  507. 

hexa-acetate,  507. 
Introduction,  1-34. 
Inulin,  269. 

Inversion.  266,  279,  283,  284,  295. 
Invertase',  286. 
Invert-sugar,  227,  266,  269,  279,  284, 

563. 

lodal,  181. 
lodo-acetic  acid,  220. 

-aniline,  p-,  462. 

-benzene,  393,  394,  523. 
dichloride,  394. 

-butane,  a-,  184. 

-phenol,  450. 

-propionic  acid,  P-,  170,  317. 
lodoform,  58.  181,  182. 

-test,  58,  182. 
lodosobenzene,  394. 
lodoxybenzene,  394. 
lonization-constant,  117. 
lonone,  177,  178. 
Iron,  Catalytic  action  of,  183,  393, 

446. 

Irone,  178. 
Isatin,  576,  578. 

chloride,  578. 
/so-amyl  acetate,  121. 
isovalerate,  121. 

-butyl  alcohol,  51.  52,  60.* 
bromopropionate,  230. 
-carbinol,  51,  62,  320. 
iodide,  153. 

-butylene,  149,  153,  154. 

-butyric  acid,  113,  224,  519. 

-camphoric  acids,  519. 

-cinnamic  acids,  445. 

-crotonic  acid,  171. 

-cvanic  acid,  345,  354,  355. 
esters,  345,  353,  355,  358. 

-cyanuric  acid,  350. 
esters,  345,  349,  35.O. 

-dibromosuccinic    acid,    213,    214, 
215. 

-eugenol,  482,  483. 

-leucine,  319,  320. 


606 


INDEX. 


/so-maltose,  291. 

-nicotinic  acid,  559,  560. 
-nitriles,  102-104,  180,  181. 
-nitroso-camphor,  518,  519. 

-ketones,  252. 
-phenylacetic  acid,  378. 
-phthalic  acid,  480,  481,  492. 
-propyl  alcohol,   51,   59,   60,   125, 

146,  186,  189. 
-amine,  83,  84. 
-benzene.     See  cumene. 
-carbinol.     See  isobutyl  alcohol. 
iodide,   44,   45,    113,    153,    189, 

190,  191. 
-purone,  369. 
-quinoline,  575,  582,  588. 

sulphate,  575. 
-saccharic  acid,  298. 
-thiocyanic  esters,  347,  348,  353. 
-urea,*  356. 

-valeraldehydeammonia,  319. 
-valeric  acid,  iso-,  277. 
Isomeric  compounds,  Physical  prop- 
erties of,  48. 
Isomerides,  42. 

Number  of  possible,  46,  47. 
Isomerism,  3,  42. 

of  the  alcohols  CnHsn+i- OH,  51,52. 
amines,  83. 
paraffins,  42-48. 
Optical,  spacial,  or  stereochemical. 

See  stereoisomerism. 
Isoprene,  162,  514,  522. 


Japan  camphor.     See  camphor. 
JULIN,  447. 

K. 

Kalkstickstoff.     See  lime-nitrogen. 
KEKULE,  380,  384. 
Keratin,  328,  330,  336. 
Keto-alcohols.     See  sugars. 
.-aldehydes,  252. 
-hexamethylene.     See    hexanone, 

cyclo-. 

-hexoses,  257,  563. 
-pentamethylene.    See   pentanone, 

cyclo-. 

-stearic  acid,  174. 

Ketone  decomposition,  301,  302,  304. 

Ketones,  60,  130-,  137,  146,  155,  158, 

159, 183,  186,  194,  224,  310,  429- 

43i. 

isonitroso-,  252. 
Mixed,  133. 


Ketones,  unsaturated,  177,  178. 
Ketonic  acids,  300-305. 

form,  308-310. 
Ketoses,  257,  258. 
Ketoximes,  135. 
Kieselguhr,  193. 
Kino-tannin,  474. 
KIPPING,  100. 
KJELDAHL,  8. 
KLASON,  350. 
KNOP,  357. 
KNOKR,  308,  570. 
KOLBE,  2,  52,  207,  470. 
KOMPPA,  520. 
KONIGS,  572,  589. 
KORNER'S  principle,  487,  488,  492. 
KOSSEL,  328,  336. 
KOSTANECKI,  VON,  472. 
KRAFFT,  172. 
KREUSSLER,  7. 
KUSTER,  239. 


L. 


Laboratory-methods,  19-34. 

Lact-albumin,  328. 

Lactams,  317. 

Lactic  acid,  223-225,  226-228,  229, 

269. 

d-,  228,  246. 
1-,  228,  246,  289. 
Racemic,  228,  246. 

fermentation,  227,  286. 
Lactide,  225. 
Lactobionic  acid,  279. 
Lactones,  221,  226,  230-232,  264,  265, 

271,  280,  527. 
Lactonitrile,  228,  316. 
Lactose,  227,  278,  279,  280. 
LADENBURG,  490,  558. 
Lsevulaldehyde,  522. 

peroxide,  522. 

Lsevulic  acid,  177,  273,  304,  305,  563. 
Laevulose,  194,  266,  267,  269-271,  279, 

281,  287,  290,  303. 
Lakes,  550. 
LASSAIGNE'S  test,  4. 
Latex,  521. 
LAURENT,  2. 

Polarimeter  of,  32,  33. 
LAUWERENBURGH,  184. 
Law  of  BERTHELOT,  28. 
dilution,  117. 

the  even  number  of  atoms,  46. 
Lead  acetate,  112,  283. 
Basic,  112. 

mercaptides,  79. 

oleate,  172. 

palmitate,  172. 


INDEX. 


607 


Lead  stearate,  172. 

Lecithin,  197. 

Lecithins,  197. 

Lecitho-prote'ins.         See     conjugated 

proteins. 
Lemonade,  249. 
Lemon-grass,  Oil  of,  176. 
Lepidine,  590. 

Leucine,  319,  320,  331,  333,  334,  336, 
338. 

iso-,  319,  320. 
LEUCKART,  417. 
Leuco-bases,  528. 

-malachite-green,  526. 
Leuconic  acid,  377,  378. 

pentoxime,  378. 
LIEBIG,  2,  5,  8,  20,  285,  344,  357. 

Condenser  of,  20,  21. 
LIEBERMANN'S  reaction,  405. 
LIEBREICH,  256. 
Light  oil,  389,  554. 

petroleum.     See  petroleum-ether. 
Lignin,  265,  294,  296. 
Ligrom,  38. 
Lime-nitrogen,  348. 

-water-test,  4. 

Limonene  nitrosochloride,  515. 
Limonenes,  513,  515. 
Linen,  294,  295. 
LINNEMAN,  Fractionating-column  of, 

23. 

Liqueurs,  268. 
Liquid  crystals,  408. 
Liquids,  Separation  of  solids  and,  30. 
LISTER,  400. 
Lithium  urate.  365. 
LORENTZ,  34. 
LORENZ,  34. 
Low  wines,  55. 
Lubricating  oil,  38. 
LUMIERE,  461. 
Lupine  seeds,  320. 
Luteolin,  472 
Lutidines,  557. 
Lyddite,  452. 
Lysine,  320,  321,  334. 


M. 

Madder-root,  548. 
Maderia,  56. 
Magenta,  141,  529,  530. 
Magnesium  halides,  Alkyl,  101,  105, 

122,  135,  314. 

Malachite-green,  525,  526,  529. 
Malei'c  acid,  210-215.  233,  242-244, 
459,  484. 

anhydride,  210,  212,  215. 


Malic  acid,  210,  232,  233.  320,  584. 
d-,  321. 
1-,  321. 
Malonic  acid,  199,  202-205.  208,  217, 

305,  364,  444. 
anhydride,  205. 
-ester  synthesis,  204,  205. 
Malonylurea.     See  barbituric  acid. 
Malt,  55,  56. 
Maltase,  281,  286. 
Maltobionic  acid.  278. 
Maltosazone,  278. 
Maltose,  54,  55,  277,  278,  280,  286, 

29i,  295. 
iso-,  291. 

Mandelic  acid,  440,  441. 
d-,  440,  441. 
I-,  246,  440. 
r-,  246,  289,  440,  441. 
Mandelonitrile,  440. 
Manneotetrose,  290. 
Mannitol,   193,   194,  262,  271,   272, 

296. 

Manno-heptonic  acid,  288. 
-nonose,  288. 

-saccharic  acid,  d-,  272,  275. 
Mannonic  acid,  d-,  272. 

i-,  272. 

Mannosazone.  d-.     See  d-glucosazone . 
Mannose,  d-,  194,  262,  271,  272,  275, 

287,  288,  295. 
i-,  272, 

hydrazone,  d-,  271. 
MARCKWALD,  246. 
Margaric  acid,  108. 
Margarine,  113. 
Margarylmethylketone,  172. 
Marsh-gas.     See  methane. 
Martius's  yellow,  540. 

MCFVENZTE,  289. 

Meconin,  588. 

Meconinic  acid,  586,  588. 

Melediose,  290. 

Mellissyl  palmitate,  122. 

Mellitic  acid,  481. 

MENDELEEFF,  57,  97. 

MENDIUS'S  reaction,  104. 

MENSCHUTKIN,  85,  402. 

Menthane,  508,  510,  516. 

Menthanol,  3-.     See  menthol. 

Menthenes,  512. 

Menthol,  246,  289,  508,  509,  513. 

Menthone,  509. 

Mercaptans,  77,  78,  79,  80,  120,  347, 

359 

Mercaptides,  78,  79. 
Mercurialis  perennis,  87. 
Mercuric  cyanide,  254,  340,  343. 

formate,  109. 


608 


INDEX. 


Mercuiic  fulminate,  296,  349,    352, 

448. 

Mercurous  formate,  109. 
Mercury  acetate,  435. 
alkides,  101. 
mercaptides,  78. 
phenide,  435. 
thiocyanate,  347. 

Mesitylene,  300,  387,  391,  490,  491. 
Mesitylenic  acid,  491,  492. 
Mesoxalic  acid,  305,  363. 
Mesoxalylurea.     See  alloxan. 
Metacet  aldehyde,  143-145. 
M eta-compounds,  384. 
Metallic  acetylenes,  39,  159. 

alkides,  100,  101. 
Meta-proteins,  326,  329,  332. 

-styrole,  443. 
Methacrylic  acid,  171. 
Methane,  34,  35-37,  40,  41,  42,  43, 
100,  112,  133,  142,  160,  179,  380, 
436. 
homologues,    Halogen    derivatives 

of,  182-185. 
-tricarboxylic  acid,  217. 
Methoxy-lutidine,  314. 

-quinoline,  p-,  590. 
Methyl  acetate,  126. 

-acetic  acid.     See  propionic  acid. 
-acetoanilide,  405. 
alcohol,   52-54,  67,  78,  85,  88,  91, 
109,    111,    125,    141,    142,   202, 
294,  309,  356,  377,  405,  406. 
-alloxan,  366. 

-allylphenylbenzylammonium    hy- 
droxide, 99. 
-amine,  84,  87,  142,  310,  342,  347, 

356,  485. 
-aniline,  404,  405,  421,  565. 

hydrochloride,  558. 
anthranilate,  476. 
-arsinic  acid,  96. 
-benzene.     See  toluene. 
bromide,  71. 
-n-butylacetic  acid,  303. 
-carbylamine,  103. 
chloride,  36,  71,  150,  389,  406. 
cyanide,  103. 
cyclo-butane,  376. 
-pentane,  505. 
-ethyl-acetic  acid.     See  valeric  acid,  \ 

Active. 

-acetylene,  160. 
-amine,  83,  87. 

-carbinol.     See  butyl  alcohol,  Sec- 
ondary. 
ether,  74. 

-ketone,  133,  134,  145,  252. 
-malonic  acid,  204,  229. 


Methyl-glucoside,  280. 

«-,  281. 

|8-,  281. 
-glyoxal,  268,  269. 

osazone,  268. 
-group,  37. 
-heptane,  2-,  48. 

3-,  48. 

4-,  48. 

-heptenone,  177. 
-indole,  3-.     See  scalole. 
iodide,  43,  44,  71,  204,  310,   376, 

405,  421,  452,  454,  495,  555,  556, 

583,  587. 
-fsophthalic      acid,      symmetrical. 

See  uvitic  acid. 

-isopropyl-benzene,     p-.     See     cy~ 
mene. 

-carbinol,  51,  162. 

-ketone,  163. 
-ketones,  134,  159,  302. 
magnesium  iodide,  511. 
-malonic  acid,  204. 
mercaptan,  78. 
-morphimethine,  587. 
-morphol,  587. 
-naphthalene,  a-,  538. 

/8-,  538. 
nitrite,  92. 

-nonylketone,  145,  303. 
-o-nitro vanillin,  553. 
-orange,  467. 

-phenyl-hydrazine,  271,   273,  421, 
570. 

bydrazones,  273. 

-pyrazolone,  570. 
-phosphine,  96. 
-phosphinic  acid,  96. 
pi  crate,  452. 
-propyl-carbinol,  51. 

-ketone,  132. 

-pyridines.     See  picolines. 
-pyrrole,  1-  (or  Ar-),  565. 

2- Cora-),  565. 

-quinoline,  p-.     See  lepidine. 
-succinimide,  585. 
sulphate.     See  dimethyl  sulphate. 
-thiophen.     See  thiotolen. 
-ureas,  356,  366. 
-violet,  530. 
Methylated  ether,  75. 

spirit,  58,  75. 
Methylene,  149,  150. 
chloride,  181,  524. 
-diphenyldiamine,  403. 
iodide,  182,  485. 
MEYER,  K.  H.,  308. 
MEYER,  R.,  478,  479. 

VICTOR,  12,  183,  500,  566,  568. 


INDEX. 


609 


MICHAEL,  125. 
MICHLER'S  ketone,  407. 
Middle  oil.     See  carbolic  oil. 
Milk,  278,  328. 

-sugar.     See  lactose. 
MILLON'S  reagent,  327. 
Mineral  acids.   Catalytic  action   of, 

125, 138, 144. 
Mixed  crystals,  247,  568. 

ketones,  133. 
Mobile  equilibrium,  Principle  of,  114, 

125- 

MOISSAN,  109. 
Molasses,  318. 
Molecular  association,  41,  53,  391. 

depression   of   the    freezing-point, 
iS,.16. 

electric  conductivity,  34. 

elevation  of  the  boiling-point,  16. 

refraction,  34. 

weight  of  carbon,  19. 
Mono-alkyl-phosphines,  95. 
-phosphinic  acids,  96. 

-basic  hydroxy-acids,  223-232. 

-bromo-.     See  bromo-. 

-carbonyl-bond,  278,  279. 

-chloro-.     See  chloro-. 

-ethyl.     See  ethyl. 

-formin,  190,  191.    . 

-halogen  compounds,  393,  394. 

-hydroxy-acids,  470-472. 

-iodo-.     See  iodo-. 

-methyl.     See  methyl. 

-nitro-.     See  nitro-. 

-stearin,  192. 

-sulphonic  acids,  397,  398. 
Monoses,  257-276,  278,  281,  286,  290, 

334. 

Monotropy,  430,  431. 
Mordants.  112,  465,  550.  580. 
Morin.  472. 
Moringa-tannin,  474. 
Morphine,  553.  586-588. 
Morus  tinctoria,  472. 
Motor-spirit,  38. 
Mucio  acid,  273,  563. 
Mucins,  329,  332. 
Murex  brandaris,  581. 
Murexide,  363. 

-test,  363. 

Muscarine,  298,  582. 
Musk,  Artificial,  449. 
Mustard-oils,  348,  359. 

-seeds,  348. 
Mutaiotation,  267. 
Myosin,  328. 

Soluble,  328. 
Myosinogen,  328. 
Myricyl  alcohol,  66. 


N. 


Naphtha,  38,  58. 

Naphthalene,  15,  373,  388,  476,  489, 

490,  534-544-  •'545,  546,  580. 
Constitution  of,  535,  536. 
-dicarboxylic  acid,  Peri-,  537. 
dihydride,  536,  541. 
-sulphonic  acid,  «-,  539. 

/?-,  539. 

Naphthaquinone,  a-,  540,  541. 
£-,  540,  541. 

amphi-  (or  2:6),  540,  541. 
-oxime,  a-,  541. 
Xaphthenes,  503. 
Naphthionic  acid,  540. 
Naphtho'ic  acid,  a-,  538. 
•     /3-,  538. 

Naphthol,  a-,  535,  538,  539. 
P-,  539. 

-disulphonic  acid,  a-,  540. 
-monosulphonic  acid,  «-,  540. 
-trisulphonic  acid,  a-,  540. 
-vellow,  540. 

Naphthylamine,  a-,  539,  540",  543. 
£-,  539,  542,  543. 
-sulphonic  acid,  1  :  4-.     See  naph- 

thionic  acid. 
tetrahydride,  a-,  543. 

18-,  542,  543. 
Narcotine,  588. 
NEF,  103,  166,  349. 
NERNST,  371. 
Neurine,  167. 
Nicotiana  tabacum,  584. 
Nicotine,  560,  564,  582,  584. 
Nicotinic  acid,  559,  560,  584. 

iso-,  559. 
Nitriles,  102-104,  127,  129,  136,  155. 

iso-,  102-104,  180,  181. 
Nitro-amine,  359. 
-amines,  355,  405. 
-aniline,  m-,  447,  451,  459,  460,  494. 
o-,  449,  459,  460. 
p-,  64,  459,  460. 
-anilines,  459,  460. 
-benz  aldehyde,  m-,  481. 

o-,  481,  552,  553. 

-benzene,  15,  27,  386,  395,  396,  399, 
403,  407,   408,  410-412,  416, 
434,  447,  448,  451,  461,  464, 
505,  529,  568,  572. 
-diazonium  chloride,  />-,  416. 
-sulphonic  acid,  m-,  449. 
o-,  449. 
p-,  449. 

-benzoic  acid,  m-,  469,  498. 
o-,  469,  498. 
p-,  469,  498. 


610 


INDEX. 


Nitro-benzoyl  chloride,  o-,  576. 

-formic  acid,  576. 
-benzyl  chloride,  p-,  532. 
-butane,  Tertiary,  92. 
-cellulose,  296,  297. 
-celluloses,  296,  297. 
-cinnamaldehyde,  o-,  573. 
-compounds,  91-94,  395,  397. 

Primary,  93. 

Secondary,  93. 

Tertiary,  93. 
-dimethylaniline,  p-,  406. 
-ethane,  91-93. 
-glycerine,  192,  193. 
-guanidine,  361. 
-4-hydroxyphenylarsinic    acid,    3-. 

462. 

-mannitol,  296. 
-mesidine,  491. 
-mesitylene,  491. 
-methane,  92,  443. 
-naphthalene,  a-,  489,  538,  539. 

0-,  539. 

-or-naphthylamine,  2-,  539. 
-paraffins,  91-94. 
-phenol,  m-,  451,  454. 

o-,  449,  451,  494. 

p-,  451,  464,  494. 
-phenols,  399,  450-452,  527. 
-phenyl-acetic  acid,  o-,  576. 

-nitromethane,  m-,  439. 
-phthalic  acid,  489. 
-propane,  Secondary,  92. 
-prus.side  test,  5. 
-pyridine,  /3-,  556. 
-salicylonitrile,  o-,  501. 
-stryrole,  443. 
-thiophen,  568. 
-toluene,  m-,  396,  495,  496. 

o-,  396,  397,  404,  469,  481,  495, 
496. 

P-,  396,  397,  404,  495,  496. 
•urethane,  359. 
-vanillin,  o-,  553. 
Nitrogen,      Quinquivalency    of,    99, 

415. 

Nitroso-amines,  86,  88,  405. 
-benzene,  410,  411,  412. 
-benzole  acid,  o-,  481. 
-camphor,  isp-,  518,  519. 
-dimethylaniline,  406,  412,  453. 

hydrochloride,  406. 
-ketones,  iso-,  252. 
-phenol,     p-.       See     benzoquinone 

mono-oxime. 
piperidine,  556. 
Nitrous-acid  test  for  amines,  86. 

nitro-compounds,  93. 
NOLTING,  492,  495. 


Nomenclature      of       the      alcohols 

CnH2n+i-OH,  51,  52. 

Nonane,  41. 

-dicarboxvlic  acid,  199. 
Nonoses,  264,  286. 
Nonyl  alcohol,  Normal,  52. 
Nonylic  acid.  108. 
Normal  chains,  45. 
Nornarcotine,  588. 
Notation,  46. 

of  Chemical   Society   of   London, 

183,  184. 

the  monoses,  267. 
Nucleic  acids,  332. 
Nucleo-prote'ins,  329,  332. 
Nucleus,  Benzene-,  385. 
Number  of  carbon  compounds,  2 ,  45. 
possible  isomerides,  46,  47. 


O. 


Oak-tannin,  474. 
Octa-decapep tides,  338. 

-peptides,  337. 
Octane,  n-,  37,  41,  48. 

cyclo-,  379. 
Octoses,  264. 

Octyl  alcohol,  Normal,  52. 
-amine,  Normal,  87,  104. 
bromide,  85. 
iodide,  Normal,  303. 
Odour,  518. 

Oil,  Fusel-,  55,  58,  60,  62,  151,*32O. 
Lubricating,  38. 
of  bitter  almonds,  380,  421. 
carraway,  380,  392,  514. 
castor-seed,  114. 
cinnamon,  444. 
citron,  176. 
cloves,  483. 
cumin,  380. 
eucalyptus,  392,  511. 
garlic,  168. 
lemon-grass,  176. 
orange-rind,  176. 
peppermint,  508,  509. 
polei,  513. 
rue,  303. 
spiraea,  482. 

the  Dutch  chemists,  184. 
thyme,  392. 

turpentine,  32,  481,  509,  514,  517. 
wintergreen,  470. 
wormseed,  511. 
olive,  31. 

Paraffin-.     See  naphtha. 
Train-,  39. 
Oils,  115,  172,  184,  191. 


INDEX. 


611 


defines,  147-157,  186,  379. 
Oleiic  acid,  114,  169,  172,  173,  174, 
191,  197. 

series  of  acids,  169-173. 
Oleum  cince,  511. 
Olive  oil,  31. 
Opium,  586. 
Optical  activity,  32,  62,  98-100. 

isomerism.     See  stereoisomerism. 
Organic  analysis,  5-11. 

chemistry,  Definition  of,  .1. 

compounds,  Classification  of,  34. 
Orientation,  385,  487-502,  537,  538, 

545,  557,  573,  574. 
Ornithine,  321,  334,  361,  479,  480. 
Ortho-acetic  acid,  111. 

-carbonic  esters,  360. 

-compounds,  384. 

-esters,  106,  180,  185,  194,  360. 

-formic  acid,  180. 
Osazones,  258,  259. 
Osmotic  pressure,  11,  14,  15. 
Osones,  271. 

OSTROMISSLENSKY,  VON,  245. 

OST'S  solution,  240,  258. 

OSTWALD,  117. 

Over-proof  spirit,  57. 
Oxalacetic  acid,  268. 
Oxalic  acid,  171,  190,  191,  199-202, 

208,  250,  282,  299,  311,  313,  340. 
Oxalis,  200. 
Oxaluric  acid,  362. 
Oxalyl  chloride,  202. 

-urea.     See  parabanic  acid. 
Oxamic  acid,  202. 
Oxamide,  202. 
Oxanthrone,  547,  548. 
Oximes,  135,  136,  431-433. 

Tautomerism  of,  310. 
Oxindole,  576. 
Oxonium  salts,  313-315. 
Oxy-cellulose,  296. 

-2  :  6-dichlpropurine,  8-,  367. 

-haemoglobin,  332. 

-methylenes,  142. 
Oxygen-carriers,  8. 

Detection  of,  5. 

Estimation  of,  9. 
Ozokerite,  39. 
Ozonides,  251,  522. 


P. 


Palmitic  acid,  108,  114,  172,  197. 
Pancreas,  192. 
Pancreatic  juice,  338. 
Papaver  somniferum,  586. 
Paper,  294,  295,  296. 


Parabanic  acid,  362,  363. 
Par#cetaldehyde,  138,  139,  143,    144, 

145- 
Para-compounds,  384. 

-cyanogen,  340. 

-formaldehyde,  142. 

-leucaniline,  529. 

-mandelic  acid,  441. . 

-myosinogen,  328. 

-rosaniline,  529. 
Paraffin,  Liquid,  31,  39. 

-oil.     See  naphtha. 

-wax,  39,  108,  114. 
Paraffines,    37,    38,    157,    390.     See 
saturated  hydrocarbons. 

Isomerism  of  the,    2-48. 

Structure  of  the,  42-47. 
Parchment-paper,  296. 
Parsley,  277. 
Partial  valencies,  384. 
PASTEUR,  241,  245,  246,  285. 
Peat,  Combustion  of,  141. 
Pelargonic  acid,  145,  173,  174. 
Penicillium  glaucum,  247,  440. 
Penta-chloro-ethane,  181,  183. 

-digalloylglucose,  474. 

-hydric  alcohols,  258. 

-methyl-aminobenzene,  406. 
-benzonitrile,  501. 
-pararosaniline.       See      methyl- 
violet. 

-methylene.     See  pentane,  cyclo-. 
-diamine,  196,  320,  555. 

hydrochloride,  196. 
dibromide,  555. 

-phenylethane,  532. 

-triacontane,  36,  41. 
Pentane,  36,  41,  46,  63,  70,  151,  157, 
182,  554. 

cyclo-,  157,  376,  377,  505. 

derivatives,  -cyclo,  376-378. 
Pentanone,  cyclo-,  376,  377,  503. 
Pentonic  acids,  258,  264. 
Pentosans,  264. 
Pentoses,  257,  264-266,  277,  290,  562, 

563. 

Penlosuria,  265. 
Pentyl  iodide,  153. 
Pepper,  559. 

Peptones,  329,  332,  333,  337,  338. 
Percentage-composition,  9-11. 
Perchloroethane.       See     hexachloro- 

ethane. 

Percolation,  583. 
Percussion-caps,  349. 
Perfumes,  Artificial,  178. 
Peri-compounds,  537. 
PERKIN,  W.  H.,  JUN.,  510,  520,  590. 

Sir  WILLIAM,  444,  484,  485,  552. 


612 


INDEX. 


Petroleum,  38,  39,  91. 
American,  38,  39. 
Caucasian,  377,  503. 
-ether,  28,  38,  101. 
Formation  of,  39,  40. 
Java,  39. 

-jelly.     See  vaseline. 
-lamp-fires,  38. 
Pharaoh's  serpents,  347. 
Phenacetin,  461. 
Phenanthraquinone,  551,  552. 
Phenanthrene,    534,    544,    55i~S53, 

586. 

-carboxylic  acid,  /3-,  553. 
Phenetole,  401,  416,  418,  461. 
Phenol,   14,   15,  388,  389,  398-400, 
401,  416,  418,  420,  450-453,  465, 
471,  482,  506,  507,  539,  566. 
-phthalem,  478,  527. 
-sulphonic  acid,  m-,  452. 
o-}  452,  453. 
p-,  452,  457. 
acids,  452. 
Phenols,  398-400,  401,  427,  481,  482, 

534. 

Phenoxides,  399,  401. 
Phenyl-acetic  acid,  440,  552. 
iso-,  378. 
pseudo-,  378. 
-acetylene,  443. 
-alanine,  334. 
-amine.     See  aniline. 
-aminopropionaldehyde,  /3-,  572. 
-anisyl-ketone,  431. 

-ketoxime,  433. 
-arsine  oxide,  434. 
-arsinic  acid,  434. 
-chloroamine,  403. 
ether,  400,  401. 

-glucosazone.     See  glucosazone,  d-. 
-glycine-o-carboxylic  acid,  579. 
-hydrazine,  136,  137,  258,  259,  273, 
278,  293,  420,  421,  428,  561, 
570. 

hydrochloride,  421. 
-hydrazones.     See  hydrazones. 
-hydroxylamine,  410,  411,  412. 
-/3-hydroxypropionic  acid,  a-.      See 

tropic  acid. 
-iodide  chloride.      See  iodobenzene 

dichloride. 
isocyanate,  438. 
magnesium  bromide,  394. 
mercury  acetate,  435. 

hydroxide,  435. 
-nitromethane,  438,  441. 
-o-aminocinnamic  acid,  a-,  553. 
-diazocinnamic  acid,  «-,  553. 
-nitrocinnamic  acid,  a-,  552. 


Phenyl-phpsphine,  434. 

-phosphinie  acid,  434. 

-phosphinyl  chloride,  434. 

-propiolic  acid,  443,  445. 

salicylate,  471. 

-salicylic  acid.  472. 

-sodionitromethane,  532. 

-tolylketone,  431. 

-vinylacetic  acid,  535,  538. 

xanthate,  417. 
Phenylene-diacetic  acid,  0-,  542. 

-diamine,  m-,  446,  448,  462,  463, 

466,  467,  492,  494. 
o-,  463. 
p-,  462,  463,  492. 

-disulphonic  acid,  m-,  454. 
Phloroglucinol,  296,  455-457. 

triacetate,  456. 

Phosgene.     See  carbonyl  chloride. 
Phosphenyl  chloride,  434. 
Phosphenylous  acid,  434. 
Phosphines,  95,  96. 
Phosphinobenzene,  433,  434. 
Phospho-benzene,  434. 

-proteins,  325,  328,  330. 
Phosphonium  bases,  Quaternary,  95, 

97. 
Photo-chemical  reactions,  544. 

-graphic  film,  297. 

-synthesis,  263. 
Phthalems,  478,  531. 
Phthalic    acid,    476-478,    489,    490, 

537,  541,  546,  547,  575,  580. 
iso-,  480,  481,  492. 
Tere-,  380,  480,  481. 

acids,  440,  476-481,  487,  505. 

anhydride,  476,  477-479,  546,  550. 
Phthalide,  477. 
Phthalimide,  475,  479,  580. 
PhthaKsoimide,  480. 
Phthalophenone,  477. 
Phthalyl  chloride,  476,  477,  480. 
Physical  properties  of  isomeric  com- 
pounds, '48. 
Picoline,  a-,  558. 

.0-,  .557,  590. 
Picolines,  557. 
Picolinic  acid,  559,  560. 
Picramide,  448,  452,  460. 
Picric  acid,  327,  448,  451,  452,  493- 

495,  524,  544. 
Picryl  chloride,  447,  452. 
Pimelic  acid,  199,  507. 
Pinacolin,  187,  533. 
Pinacone,  186,  187,  533. 
Pinacones,  186. 
Pinane,  516. 
Pinene,  517,  518. 
Pinic  acid,  518. 


INDEX. 


613 


"Pink  salt,"  465. 
Pinonic  acid,  518. 
Piperic  acid,  484,  485,  559. 
Piperidine,  90,  196,  555,  556,  559. 
Piperine,  484,  559. 
Piperonal,  483,  484,  485. 
Piperonylacraldehyde,  485. 
Pitch,  389. 
Platinotypes,  202. 
Polarimeter,  LAUUENT'S,  32,  33. 
Polarimetry,  32,  33,  283,  284. 
Poly-ammo-compounds,  462-468. 

-basic  acids,  198-218,  476'-481. 
hydroxy-acids,  248,  249. 

-halogen  derivatives,  179-185,  446, 
447. 

-hydric  alcohols,  185-194. 
phenols,  453-457. 

-methylene   compounds.     See   all- 
cyclic  compounds. 

-nitro-derivatives,  448,  449. 

-oxymethylene,  a-,  142. 
/3-,  142. 
7-,  142. 
6-,  142. 

-pep tides,  337-339. 

-sulphonic  acids,  449,  450. 

-terpenes,  521,  522. 
Polymerization,  139,  142,  143. 

of  aldehydes,  138-145. 
Polyoses,  257,  262,  264,  266,  289-297, 

334. 

POPE,  98-100. 
Port,  56. 

Potash-bulbs,  6,  7. 
Potassiopyrrole,  564,  566. 
Potassium  acetate,  207,  267,  306,  441. 

alkides,  100. 

anilide,  404. 

antimony  1  d-tartrate,  238. 

benzenesulphonate,  398,  422. 

benzoate,  427. 

carbazole,  544. 

carbonyl,  457. 

copper-propiolate,  217. 

cuprous  cyanide,  417. 

cyanate,  340,  345,  354,  357,  365. 

cyanide,   102,   104,   134,   169,   171, 
'180,    196,    202,    206,    217,    249, 
340,    343,    422,    440,   533,    562, 
574. 

diacetylenedicarboxylate,  217. 

ethoxide,  67,  353. 

ethysulphate,  73,  78,  79,  102. 

ferric  oxalate,  201,  202. 

ferricyanide,  217. 

ferrocyanide,   102,   104,  341,   343, 

344- 
ferrous  oxalate,  201 . 


Potassium  formate,  200,  343. 

glycollate,  220. 

hydrogen    acetylenedicarboxylate, 

216. 

mesotartrate,  243. 
saccharate,  267. 
o-sulphobenzoate,  470. 
d-tartrate,  238. 

monochloroacetate,  202. 

oxalate,  200. 

phthalaminate,  475. 

phthalimide,  479. 

propiolate,  216. 

d-tartrate,  238.  _ 

tetra-acetylenedicarboxylate,  217. 

thiocyanate,  346,  347. 

trithiocarbonate,  352. 

xanthate,  353,  417. 
Potato-starch,  291,  293,  294. 
Presssaft,  285. 

Primary  alcohols,  52,  60,  61,  107,   125, 
130,  133,  147. 

amines,  83,  84,  86,  87,  91,"104,  136, 
181,  355,  401-404. 

arsines,  96. 

carbon  atoms,  46. 

compounds,  52. 

nitre-compounds,  93. 

phosphines,  96; 

reduction-products,  410. 
Principle  of  mobile  equilibrium,   114, 

125. 

the  counter-current,  282. 
PRING,  36. 
Producer-gas,  53. 
Proline,  335,  336. 
Proof-spirit,  57,  58. 
Proponal,  cyclo-,  376. 
Propane,  36,  37,  41,  42,  44,  45,  183. 

cyclo-,  375,  379. 

-tricarboxylic    acid,    a.$a!-.        See 

tricarballylic  acid. 
Propargyl  alcohol,  166,  168. 

compounds,  166. 
Prophenylpyridine,  a-,  558. 
Properties  of  alcohols,  CnHz/i+i-OH, 

52,  53. 
Propiolaldehyde,  176. 

-acetal,  176,  569. 
Propiolic  acid,  168. 

series  of  acids,  173,  174. 
Propionaldehyde,  59,  132,  134,  153, 

165. 
Propionic  acid.  59,  60,  102,  103,  108, 

112,  117,  118,  142,  145,  160,  170, 

220,  225,  229,  300. 
Propionitrile,  103. 
Propionyl-group,  109. 
Propyl-acetylene,  160. 


614 


INDEX. 


Propyl  alcohol,  iso-,  51,  59,   60,  125, 

146,  186,  189. 
Normal,  51,  52,  59,  60,  74,  125, 

165,  168. 
-amine,  iso-,  83,  84. 

Normal,  83,  84,  87. 
-benzene,  iso-.     See  cumene. 
bromide,  Normal,  71,  85. 
-carbinol,  iso-.     See  isobutyl  alco- 
hol. 

Normal.     See  butyl  alcohol,  Nor- 
mal. 

-carbpxylic  acid,  cyclo-,  171,  375. 
chloride,  Normal,  71. 
derivatives,  cyclo-,  375. 
-dicarboxylic  acid,  cyclo-,  375. 
-group,  37. 
iodide,  iso-,  44,  45,  113,  153,  189, 

191. 

Normal,  44,  45,  71,  113,  153. 
-piperdine,  a-,  558,  559. 
0-,  559. 
7-,  559. 

-pseudomtrole,  93. 
Propylene,  148,  152,  153,  184,  189, 

191,  375,  509,  515. 
chloride,  153,  165,  189. 
-glycol,  223,  227. 
Propylidene  chloride,  153,  164. 
Prosthetic  group,  328,  329. 
Protamines,  328. 
Proteans,  329. 

Protein-derivatives,  329,  330,332,333. 

Proteins,   2,  54,   55,   143,  282,  283, 

286,  287,  288,  316,  318,  320,  325- 

339,    361,    400,  474,  483,  557,  564, 

577,  586. 

Proteoses,  329,  333. 
Protocatechualdehyde,  482,  484. 
Protocatechuic  acid,  472,  473,  485. 
Protoplasm,  282,  285, -287. 
Prussian-blue  test,  4. 
Prussic  acid.     See  hydrocyanic  acid. 
PSCHORR,  552. 

Pseudo-acids,  438-440,  527,  548. 
-bases.    See  colour-bases. 
-ionone,  177. 
-nitroles,  93. 

-racemic  mixed  crystals,  247,  248. 
-uric  acid,  365. 
Ptomaines,  196,  333. 
Pulegone,  512,  513. 
Purine,  365,  367. 
Purone,  369. 

iso-,  369. 

"  Purple  of  the  ancients,"  581. 
Purpurin,  550. 

Putrescine.         See       tetramethylene- 
diamine. 


Pyknometer,  32. 
Pyrazole,  324.  374,  568-570. 
Pyrazoline,  570. 
Pyrazolone,  570. 

Pyridine,  259,  272,  307,  373,  388, 
389,  554-56o,  573,  582,  584, 
585,  588. 

-carboxylic  acids,  559,  560. 

ferrocyanide,  554. 

-sulphonic  acid,  554. 

-tricarboxylic  acid,  afiy-,  590. 
Pyro-catechin  or  pyrocatechol.     See 
catechol. 

-gallic  acid.     See  pyrogallol. 

-gallol,  455,  473. 

-mellitic  acid,  481. 
anhydride,  481. 

-mucic  acid,  562-564. 

-racemic  acid,  224,  238,  268,  300, 
301. 

-tartaric  acid,  238. 
Pyrone  derivatives,  311-315,  478. 

-dicarboxylic  acid.     See  chelidonic 

acid. 
Pyrrole,  374,  555,  564-566,  577. 

-carboxylic  acid,  2-,  566. 

-red,  564. 

"  Pyri olidin."     See  tetrahydro  pyrrole. 
"Pyrrolin."     See  dihydropyrrole. 
Pyruvic  acid.     See  pyroracemic  acid. 


Q- 


Quadrivalent  oxygen,  313. 
Quadroxalates,  201. 
Qualitative  analysis,  3-5. 
Quantitative  analysis,  5-11. 
Quaternary  ammonium  bases,  83,  84, 
407. 

arsonium  bases,  96. 

carbon  atoms,  46. 

phosphonium  bases,  95. 

stibonium  bases,  97. 
Quick  process  for  vinegar,  110. 
Quina-red,  589. 
Quinhydrone,  457. 
Quinine,  440,  475,  589,  590. 

-tannin,  474. 
Quinitol,  506. 

as-,  506,  507. 

trans-,  506,  507. 
Quinol,  454,  455,  457,  463,  526. 
Quinoline,  272,  374,  389,  509,  554, 
555,  560,  572-755,  582,  589,  590. 

dichromate,  572. 

wo-,  575 »  582,  588. 

sulphate,  iso-,  575. 

-sulphonic  acids,  574. 


INDEX 


615 


Quinolinic  acid,  560,  573. 
Quinone.     See  benzoquinone. 

di-imide,  463. 
Quinones,  457-459,  545,  548. 

o-,  453. 

Quinonoid  forms,  526,  527. 
Quinotannic  acid,  589. 
Quinovic  acid,  589. 
Quinovin,  589. 
Quinoxalines,  463. 


R. 


Racemic  acid .     See  tarlaric  acid,  r- 

substances,  228,  241. 

Resolution  of,  245-248. 
Racemoids,  247. 
Raffinose,  289,  290. 
Raphides,  200. 
Reactions,  Bimolecular,  85,  125,  126. 

Reversible,  122,  138. 

Unimolecular,  126. 
Reagent,  SCHIFF'S,  141. 
Reduction-products,  Chemical  or  sec- 
ondary, 410. 

Electrolytic  or  primary,  410. 
Reflux-condenser,  20. 
Refraction,  33,  34,  148,  156,  157,  308, 
440,  521,  543,  544. 

Atomic,  157. 

Index  of,  33. 

Molecular,  34,  157,  410,  521,  543, 

544. 

Refractive  power..    See  refraction. 
REIMER'S  synthesis,  482,  483. 
REMSEN,  470. 
Rennet,  328. 
Resinification,  139,  140. 
Resorcin.     See  resorcinol. 

-yellow,  467. 

Resorcinol,  449,  454,  455,  458,  467, 
478,  563. 

-phthalei'n.     See  fluorescein. 
Reversible  reactions,  122,  138. 
Rhodium,  Catalytic  action  of,  1 10. 
Rice-starch.  292~ 
RICHTER,  374. 
Ritinus  communis,  114. 
Rigor  mortis,  328. 

Ring    compounds.     See    cyclic    com- 
pounds. 

ROBINSON,  590. 
Rodinal,  461. 

ROOZEBOOM,  BAKHUIS,  248. 
Rosaniline,  465,  529,  530. 
Rosanilines,  525-531. 
ROSENIIEIM,  328. 
Rosolic  acid,  530,  531. 


Rotation  of  plane  of  polarization,  32, 

33,  62. 

Rotatory  power,  Specific,  32,  33. 
Ruberythric  acid,  548. 
Rum,  56. 

Ruta  graveolens,  303. 
Rye-starch,  292. 


S. 


SABATIER,  35,  151,  504,  506. 
Saccharates,  261,  281,  282. 
Saccharic  acid,  d-,  267,  276. 

iso-,  298. 

Saccharides.     See  sugars. 
Saccharification,  55. 
"Saccharin,"  469,  470. 
Saccharose.     See  sucrose. 
SAINT  GILES,  PEAN  DE,  122. 
Salicin,  470. 
Salicylaldehyde,  482. 
Salicvlic  acid,  470-472,  492,  493,  566, 

571. 

Saligenin,  470. 
"Salipyrine,"  571. 
Salmine,  328,  336. 
"Salol,"  471. 
"Salt  of  sorrel,"  201. 
"Salting-out,"  115,  326,  330,  466. 
"Salvarsan,"  462. 
SANDMEYER,  416. 
Saponification,  125-127. 

of  fats,  113,  114,  115,  126. 
Sarcolactic  acid,  228. 
Saturated    hydrocarbons,    CnH2n+2, 

35-48,    100,    148,    157,    179,  185, 

379.     See  paraffins. 
Sauerkraut,  227. 
Sawdust,  200. 
Scatole,  333,  335,  577. 
SCHIFF'S  reagent,  141,  255,  281. 
Schizomycetes,  285. 
Schizosaccharomyces  octosporus,  286. 

SCHORLEMMER,  70. 

Sclero-proteins,  328,  330,  331. 
SCHMIDT,  470. 

SCHUTZENBERGER,  333-335. 

SCHWEITZER'S  reagent,  295,  297. 
Scutching,  295. 
Sebacic  acid,  199. 

Secondary    alcohols,    52,    61,     125, 
130-133,  135,  147. 

amines,  83,  84,  86,  87,  104. 

arsines,  96. 

carbon  atoms,  46. 

compounds,  52. 

mtro-compounds,  93. 

phosphines,  96. 

reduction-products,  410. 


616 


INDEX. 


Selenium  compounds,  81 . 
Semi-carbazide,  357. 

-carbazones,  357. 
Semidine-transformation,  409. 
SENDERENS,  35,  76,  150,  504-506. 
SENIER,  189,  344,  350. 
SENTER,  322. 
Separating-funnel,  28. 
Separation  of  amines,  86. 

immiscible  liquids,  28-30. 
solids  and  liquids,  30. 

from  one  another,  30. 
Sericin,  331. 
Sericom,  338. 
Serine,  334. 
SERTURNER,  586. 
Serum-albumin,  326,  328. 

-globulin,  328. 
Sherry,  56. 
Side-chain,  48,  385. 
Silicanes,  98. 
Silicoheptane,  98. 
Silicon  alkides.     See  silicanes. 

atomes,  Asymmetric,  100. 

Chemistry  of,  98. 

tetraethide,  98. 
Silk,  Artificial,  297. 

-gum.     See  sericin. 
SILVA,  189. 
Silver  acetate,  107,  185,  186. 

acetylene,  159. 

cyanamide,  348. 

cyanate,  345. 

cyanide,  341,  576. 

cyanurate,  350. 

formate,  109. 

fulminate,  349. 

laeyulate,  273. 

-mirror-test,  141. 

picrate,  452. 

thiocyanate,  347. 
SIMPSON,  180. 
SKRATIP,  572,  574,  589. 
Sleeping  sickness.     See  trypanosomia- 

sis. 

Smokeless  powder,  297. 
Soap,  Green,  115. 

Hard,  115. 

Potassium-,  115. 

Sodium-,  115. 

Soft,  115. 
Soaps,  115,  116. 
Soda-lime-test,  4. 
Sodamide,  253,  539. 
Sodio-acetylacetone,  306. 

-rc-amylacetylene,  253. 

-dinitroethane,  439,  440. 

-nitro-ethane,  92. 

-propane,  Seconda^,  92. 


Sodio-phenyl  nitrom ethane,  438. 

-z'sonitromethane,  438. 
Sodium  acetate,  105,  112,  260,  444, 
485. 

acetylene,  173. 

alkides,  100,  105. 

ammonium  racemate,  245,  248. 

rf-tartrate,  245. 

Z-tartrate,  245. 

anthraquinonesulphonate,  549. 

benzoate,  422,  425. 

cyanide,  343. 

diazobenzenesulphonate,  420. 

ethoxide,  66,  67,  92,  180,  185,  204, 
205,  252,  253,  302,  321,  367,  448, 
455. 

formate,  200. 

hydrogen  urate,  365. 

methide,  105. 

methoxide,  66,  67,  74,  92,  106,  310, 
394,  447,  448. 

-nitroprusside-test,  5. 

oxalate,  200. 

-p-acetylaminophenylarsinate.  See 
arsacetin. 

-aminophenylarsinate.     See  atoxyl. 

phenoxide,  399,  401,  470,  471,  565. 

phenyl-carbonate,  471. 
-hydrazinesulphonate,  420. 
-salicylate,  471. 

stearate.  107. 

sulphanilate,  460. 

urate,  365. 
Solubility-curve  for  two  liquids,  89. 

-curves     for     triethylamine     and 

water,  89. 
Soluble  myogen-fibrin.     See  myosin, 

Soluble. 
Solvents,  Cryoscopic,  14,  15,  16. 

Ebullioscopic,  16. 

Extraction  with,  28. 
Soporifics,  146,  254,  256,  429. 
Sorbitol,  d-,  262. 
Sorbose-bacteria,  262. 
Spacial  isomerism.     See  stereoisomer- 

ism. 

Specific   gravity,    Determination   of, 
32. 

rotatory  power,  32,  33. 
Spent  lees,  55. 

wash,  55. 
Spermaceti,  66. 
Spirits,  55. 

of  wine,  56. 
Spongin,  331. 

Starch,  54,  263,  266,  269,  277,  291- 
294,  295. 

Manufacture  of,  294. 
Steam-distillation,  26-28. 


INDEX. 


617 


Stearic  acid,  15,  108,  114,  172,  191, 

192. 

Structure  of,  172. 
"  Stearine,"  114. 

candles,  114. 
Stearolic  acid,  173,  174. 
Stearyl  alcohol,  107. 
Stereochemical  isomerism.  See  stereo- 

isomerism. 
Stereochemistry  of  the  monoses,  273- 

276. 

Stereoisomerism,  64,  65.  66,  210-215, 
221-223.  228-230,  233-238,  273- 
276,  321-323,  339,  431-433,  444, 
445. 

of  nitrogen,  431-433. 

VAN  'T  HOFF'S  theory  of,  64-66. 
Stibines,  97. 

Tertiary,  97. 

Stibonium  bases,  Quaternary,  97. 
Stilbene,  532,  552. 
Storax,  443. 
Strain-theory,    VON    BAEYER'S,  156, 

209. 

Straw,  266,  295. 
STRECKER,  316. 
Strength  of  acids,  118. 
Strong  hydrolysis,  301. 
Structural  or  constitutional  formula , 

44,  51. 

Str-uettire  of  the  paraffins,  42-48. 
Strychnine,  246,  475,  590. 

i-mannonate,  272. 
Strychnos  nux  vomica,  590. 
Sturine,  328. 
Styphnic  acid,  454. 
Styrole,  443. 

Suberanecarboxylic  acid,  378,  379. 
Suberic  acid,  199. 
Suberone,  378,  379,  585. 
Substitution,  36,  229. 
Succindialdehyde,  251,  564,  565. 

Oxime  of,  565. 

Succinic  acid,  29,  30,  54,  199,  205, 
206,  208,  209,  210,  215,  231,  233, 
238,  567. 

anhydride,  208. 
Succinimide,  209. 
Succinonitrile.  See  ethylene  cyanide. 

J,  32,  113,  200,  227,  248,  265, 
),  279-284,  285,  286,  290,  563. 
Manufacture  of,  282,  283. 
Quantitative    estimation    of,    283, 

284. 

Velocitv  of  inversion  of,  284. 
Sugar-beet,  265,  279,  282,  283,  318. 
-cane,  279. 
Cane-.     See  sucrose. 
of  lead.     See  lead  acetate. 


Sugars,  257-297,  320;  325,  328,  332, 

586. 

Sulphaminobenzoic  acid,  p-,  470. 
Sulphanilic  acid,  457,  460,  462. 
Sulphinic  acids,  Alkyl-,  80. 
Sulphite-method,  295. 
Sulpho-benzene  diazonium   chloride, 
p-,467. 

-benzole  acid,  m-,  469. 

o-,  470. 
acids,  469,  470. 

-cyanic  acid.     See  thiocyanic  acid. 
Sulphonal,  146. 
Sulphonamides,  398. 
Sulphones,  80,  374. 
Sulphonic  acids,  80,  449,  450,  452, 

460,  469,  470. 

Sulphonium    compounds,    Asymme- 
tric, 98. 
Sulphonyl  chlorides,  Alkyl-,  80. 

Aromatic,  397. 
Sulphonium  halides,  79. 

hydroxides,  79. 

iodides,  79. 
Sulphoxides,  80. 
Sulphur,  Estimation  of,  8. 
Supertension,  371. 
Symmetrical  compounds,  385. 
Syntonins.     See  meta-proielns. 


T. 


TAFET,,  368,  370. 

Tanacetone.     See  thujone. 

Tannic  acids.     See  tannins.      * 

Tannin,  291,  327,  331,  474,  475,  583. 

Tanning,  475. 

Tannins,  474,  475. 

TANRET,  267. 

Tar,  388,  389,  391,  398,  534,  544,  554, 

566,  572,  575. 
Wood-,  54. 

'•  Tartar-emeti. ,"  238. 
Tartaric  acid,  d-,  233,  234,  235,  236, 
237,  238,  240,  241,  242,  245, 
247,  268,  289,  300. 
1-,  233,  234,  236,  237,  240,  245, 

247,  289. 
Meso-,  233,  234,  237,  240,  241- 

243,  276. 
r-,  233,  234,  238,  249,  241,  242, 

243,  247,  300. 
acids,  233-245,  287. 
Tartronic  acid,  188,  232. 
Tautomerism,  305-310,  339,  548. 
Tea,  366,  473,  474,  583. 
Tellurium  compounds,  81. 
Terephthalic  acid,  380, 480. 481. 


618 


INDEX. 


Terminal  carbon  atoms,  46. 
Terpenes,   378,   392,   503,   508,   518, 

521,522. 
Terpin,  509-511,  512,  514. 

hydrate,  500,  510,  512. 
Terpineol,  512,  513,  514,  518. 
Terpinolene,  513,  514. 
Tertiary  alcohols,  52,  61,  122,   125, 

135,  147. 

amines,  83,  84,  86,  87, 104. 
arsines,  96,  97. 
bismuthines,  97. 
carbon  atoms,  46. 
compounds,  52. 
nitro-compounds,  93. 
phosphines,  96. 
Tervalency  of  carbon,  532. 
Test,  BEILSTETN'S,  5. 

Carbylamine-,  103,  104,  403. 
Copper-oxide-,  4. 
Jodoform,  58,  182. 
LASSAIGNE'S,  4. 
Lime-water-,  4. 
Prussian-blue-,  4. 
Silver-mirror-,  141. 
Soda-lime-,  4. 
Sodium-nitroprusside-,  5. 
Test  for  absolute  alcohol,  56,  57,  91. 
acetates,  Cacodyl-,  97,  112. 

Ferric-chloride,  112. 
amines,  Nitrous-acid-,  86. 
anthraquinone,  547. 
blood,  332. 
cellulose,  295. 
cycfohexanone,  507. 
dextrose,  267. 
double  bonds,  Optical,  157. 

VON  BAEYER'S,  148. 
glycerol,  189. 
hexoses,  273. 

identity  of  substances,  31. 
ketoses,  271. 
lignin,  294,  296. 
nitric  acid,  404. 
nitro-compounds.   Nitrous-acid-, 

93. 

nitrous  acid,  463,  467. 
pentoses,  266. 
phenols,  399,  400. 
phthalic  acid,  478. 
anhydride,  478. 
primary  amines,  HOFMANN'S,  87, 

103,  104. 
pyrrole,  564. 
resorcinol,  478. 
starch,  291. 
xylose,  266. 
Tests  for  aldehydes,  141. 

amines,  86,  87,  101,  102. 


Tests  for  aniline,  403,  404. 

ethyl  alcohol,  58,  182,  425. 
hydroxyl-group,  49,  50,  119/120. 
monoses,  258,  259.  1 

primar}',  secondary,  and  tertiary 

alcohols,  61 . 
proteins,  327. 

tautomeric  forms,  308-310. 
Tetra-acetylenedicarboxylic  acid,  217. 
-alkylammonium  iodides,  Velocity 

of  formation  of,  85. 
-bromo-ethane,  545. 
-fluorescei'n,  478. 
-methane.      See  carbon  tetrabro- 

mide. 

-chloro-ethane,  183,  184. 
-ethylene,  181,  183. 
-methane.   See  carbon  telrachlo- 

ride. 

-decane,  41. 

-ethyl-ammonium  hydroxide,  88. 
disodioethanetetracarboxylate, 

535. 
hvdronaphthalenetetracarbox- 

ylate,  535. 
-methane,  38. 
orthocarbonate,  360. 
-hydro-benzene,  506. 
-pyrrole,  566,  585. 

-carboxylic  acid.     See  proline. 
-hydroxyflavone,  1:3:2':  4'-.    See 

morin. 

1  :3:3':4'-.     See  luteolin. 
-methyl-ammonium  hydroxide,  88. 
-butane,  2:  2':  3:  3'-,  48. 
-diamlnobenzophenone,  407. 
-triphenyl-carbinol,  526. 

-methane,  526. 
-succinic  acid,  219. 
-uric  acid,  368. 

-methylene.     See  butane,  cyclo-. 
bromide,  376. 
-diamine,  196,  322. 
-nitrophenol,  2:3:4:6-,  454. 
peptides,  337. 
Tetrolic  acid,  174. 
Tetroses,  264,  290. 
Thei'ne.     See  caffeine. 
Theobromine,  365-367,  582. 
Theory  of  stereoisomerism,    VAN    'T 

HOFF'S,  64-66. 

Thermometers,  Abbreviated,  32. 
THCELE,  31,  163,  383,  384,  536. 
Thienylmethylketone,  2-.     See  aceto- 

thi'enone. 
Thio-acids,  127. 

-cyanic  acid,  346,  347. 
esters,  347,  348. 
iso-,  347,  348,  353. 


INDEX. 


619 


Thio-ethers,  77-79,  80. 

-indigo,  581. 

-methylene,  348. 

-phenol,  386. 

-tolen,  566,  568. 

-urea,  359,  360. 
Thiophen,  374,  566-568. 

carboxylic  acid,  2-,  568. 
3-,  568. 

Dimethol-.     See  Ihioxen. 

mercuiyoxy acetate,  566. 

Methyl-.     See  thioiolen. 
Thiophensulphonic  acid,  568. 
Thioxen,  566,  567. 
THORPE,  520. 
Thujone,  521. 
Thymol,  400,  509. 
TICKLE,  313. 
Tiglic  acid,  169. 
Tin  atoms,  Asymmetric,  ICO. 

ethide,  101. 
Toadstool,  298. 
Tolan,  532. 

Toluene,  380,  388,  389,  390,  391,  396, 
397,  400,  422,  436-438,  469,  495, 
566. 

-sulphamide,  o-,  469. 

-sulphonic  acid,  m-,  498. 
o-,  498. 
p-,  498. 

-sulphonyl  chloride,  o-,  469. 

p-,  469. 

Toluic  acids,  426,  440. 
Toluidine,  ra-,  495. 

o-,  404,  495,  529. 

p-,  15,  404,  495,  529,  558,  565. 

hydrochloride,  p-,  406. 
Train-oil,  39. 
Triacetoneamine,  145. 
Trialkyl-phosphines,  95. 

-phosphine  oxides,  96. 
Triamino-azobenzene,  466,  467. 

-benzenes,  463. 

-triphenyl-carbinol,  529. 
Triamylene,  151. 
Trianisvlcarbinol,  527. 
Tribasic  acids,   217,   218,   248,   249, 

481. 

TRIBE.     See  GLADSTONE. 
Tribenzoyladrenaline,  485. 
Tribenzylamine,  441. 
Tribromo-aniline,      2:4:6-,      402, 
459. 

-hydrin,  168,  183,  189,  217. 

-phenol,  2:4:6-,  399,  450. 

-resorcinol,  454. 
Tricalcium  saccharate,  282. 
Tricarballylic  acid,  217,  218. 
Trichloro-acetal,  254,  255. 


Trichloro-acetaldehyde.     See  choral. 

-acetic  acid,  125,  220,  221,  255. 

-ethylene,  183,  184. 

-hydrin,  189. 

-phenol,  450. 

-purine,  2:6:8:-,  367. 
Tricosane,  41. 
Tridiphenylmethyl,  532. 
Triethyl-amine,  85,  88,  89,  90. 

-arsine,  96. 

-bismuthine,  97. 

citrate,  247. 

-methane,  98. 

-phosphine,  96. 
oxide,  95,  96. 

pyrazoletricarboxylate,  569. 

pyrazolinetricarboxylate,  570. 
Trihalogenbenzenes,  1:2:4-,  446. 
Trihydric  alcohols,  188-193. 

phenols,  455-457. 
Trihydroxy-acids,  473-475. 

-anthraquinone,  5  :  6  :  8-.     See 
purpurin. 

-glutaric     acid,    265,      270,    274, 

275. 
Tri-iodo-hydrin,  190. 

-phenol,  507. 
Triketohexamethylene.     See    phloro- 

glucinol. 
Trimethyl-acetic  acid,  219. 

-acetyl  chloride,  187. 

-amine;  83,  87,  88,  142,  167,  197, 
319,  376. 

-carbinol,  51,  61,  125,  135. 

-ethylene,  162. 

-glyciae,  318. 

-oxonium  iodide,  314. 

-phloroglucinol,  457. 

-phosphine  oxide,  96. 

-pyridines.     See  collidines. 

-succinic  acid,  519. 
Trimethvlene.     See  propane,  cyclo-. 

bromide,  184,  185,  196,  375,  479. 

cyanide,  196. 

-diamine,  196. 

-glycol,  185. 

diacetate,  185. 

Trinitro-aniline,      2:4:6-.          See 
picramide. 

-benzene,  Symmetrical,  448,   495, 
502. 

-butylxvlene,  449. 

-cellulose,  296. 

-oxy cellulose,  296. 

-phenol,     2:4:6-.       See     picric 

acid. 

Trioses,  257,  262,  264.  286. 
Tripeptides,  337. 
Triphenyl-amine,  402,  405. 


620 


INDEX. 


Triphenyl-carbinolcarboxylic       acid; 
477. 

-chloromethane,  531. 

methane,  407,  427,  478,  525. 
dyes.     See  rosanilines. 

-methyl,  531,  532. 
iodide,  531. 
peroxide,  531. 

-rosaniline  hydrochloride.    See  ani- 
line-blue. 

Tristearin.  191,  192,  338. 
Trithio-carbonic  acid,  352. 

-methylene,  348. 
TROOSTWYK,  PAETS  VAN,  184. 
Tropic  acid,  584,  585. 
Tropidine,  585. 
Tropine,  584,  585. 

-carboxylic  acid.     See  ecgonine. 
Trypanosomiasis,  462. 
Tryptophan,  305,  577. 
Tube-furnace,  8,  9. 
Turkey-red,  550. 
Tyrian  purple,  581. 
Tyrosine,   331,   333,   334,   336,   338, 

483- 


U. 


Undecane,  41. 
Undecylenic  acid,  169. 
Under-proof  spirit,  57. 
Unimolecular  reactions,  126. 
Unsaturated  acids,  Monobasic,  169- 
174. 

alcohols,  166-168. 

aldehydes,  175-178. 

compounds,  148. 

dibasic  acids,  210-217. 

halogen  compounds,  164-166. 

hydrocarbons,    76,  147-163,    379, 
443. 

ketones,  177,  178. 
Unsymmetrical  compounds,  385. 
Uranium  oxalate,  201. 
Urea,  1,  349,  352,  353~357,  363,  366. 

iso-,  356. 

nitrate,  354,  355. 

oxalate,  355. 
Ureides,  362. 
Urei'do-acids,  362. 
Urethane,  15,  358,  359. 
Urethanes,  358,  359. 
Uric  acid,  305,  362-368,  369. 

group,  362-371. 
Urine,  146,  353,  354,  357,  365. 
Urochlorah'c  acid,  256. 
"Urotropine,"  142. 
Uviol  lamp,  445. 
Uvitic  acid,  300,  480. 


V. 


Vacuum-distillation,  21,  22. 
Valency  of  carbon,  19,  64,  99,  103, 

151-155,  166,  532. 
Valeraldehyde,  132. 

-ammonia,  iso-,  319. 
Valeric  acid,  62,  108,  118,  333. 
Active,  204,  229. 
iso-,  277. 

Valerolacetone,  221. 
Valeryl-group,  109. 
Vanilla,  380,  482. 
Vanillin,  482,  483. 
Vapour-density    apparatus,    VICTOR 

MEYER'S,  12. 
Determination  of,  12,  13. 

VICTOR  MEYER'S  method  for, 

12,  13. 

Vaseline,  38,  39. 
Vat-dyeing,  580. 

-dyestuffs,  580?  581. 
Vegetable-fats,  34,  113. 

-ivory  nut,  271. 
Velocity  of  formation  of  tetra-alkyl- 

ammonium  iodides,  85. 
Veratrole,  454. 

Vesuvine.     See  Bismarck-brown. 
Vicia  augustifolia,  277. 
Vicianin,  277. 
Vicianose,  277. 
Vicinal  compounds,  385. 
VILLIGER,  314. 

Vinegar,   German  or  Quick  process 
for,  1-10. 

-manufacture,  110. 
Vine-lice,  352. 
Vinyl-acetic  acid,  171. 

alcohol,  166,  167. 

bromide,  164,  165,  166. 

chloride,  165,  166. 

-ethylene,  157. 

-group,  167. 
Violets,  178. 
Violuric  acid,  364. 
Viscose,  297. 
Viscosity,  111. 
Vital  force,  1. 
Vitellin,  328. 
Volatile  fatty  acids,  113. 
VOLHARD,  347. 
VORLANDER,  408. 
Vulcanite,  521. 
Vulcanization,  184,  352,  521. 

W. 

WADMORE,  350. 
WALDEN,  230,  321-323. 
inversion,  321-323. 


INDEX. 


621 


WALKER,  JAMES,  354. 
Wax,  66. 

Earth-,  39. 

Paraffin-,  39,  108,  114. 
Weak  hydrolysis,  301. 
WEIGEL,  20. 
Weld,  472. 
WERNER,  99,  322. 
Whey,  278. 
Whisky,  56. 
White  lead,  112. 

WlLFARTH,  8. 

WILLIAMSON,  Ether-synthesis  of,  74. 

WlLLSTATTER,  585. 

Wine,  56,  110. 

Spirits  of,  56. 
Wines,  Fortified,  56. 

WlNKLER,  97. 
WlSLICENUS,  252. 

WITT,  464. 

WOHLER,  1,  2,  344,  354,  355. 

WOLLASTON,  335. 

Wood,  265,  295,  296. 

-charcoal,  481. 

Combustion  of,  141. 

Distillation  of,  53,  54. 

-spirit,  54,  58,  146. 

-sugar.     See  xylose. 

-tar,  54. 
Woodruff,  484. 
WURTZ,  23,  346. 

Fractionating  column  of,  23. 

X. 

Xanthic  acid,  353. 
Xanthine,  332,  365-369. 


Xantho-chelidonic  acid,  311,  312. 

-protein-reaction,  327,  330,  333. 
Xanthone,  472. 

dyes,  472. 
Xylene,  m-,  391,  39*,  491,  492. 

o-,  392,  488,  489. 

p-,  392,  492. 

Xylenesulphonic  acids,  392. 
Xylenes,  389,  390,  487,  566. 
Xylic  acids,  426. 
Xylidines,  404. 
Xylitol,  193,  262,  265. 
Xylonic  acid,  265. 
Xylose,  262,  264,  265,  274. 
Xylylene  bromide,  o-,  535. 


Y. 


Yeast,  55,  285,  320. 

-cells,  54,  285,  286. 
YOUNG,  SIDNEY,  23,  41,  42,  53. 

Formula  of,  41,  42,  53. 

Fractionating-column  of,  23. 


Z. 


ZELINSKY,  505. 

Zinc  alkides,  100,  101,  105.  133. 

ethide,  100. 

lactate,  227. 

methide,  100,  133.  187. 

propide,  100. 
Zymase,  286. 


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